Positive resist composition and pattern forming method using the same

ABSTRACT

A positive resist composition, which comprises: (A) a resin having a monocyclic or polycyclic alicyclic hydrocarbon structure, of which solubility in an alkali developer increases under an action of an acid; (B) a compound capable of generating an acid upon irradiation with actinic rays or radiation; (C) a resin having a repeating unit represented by formula (C) as defined in the specification; and (D) a solvent, wherein a content of the resin as the component (C) is from 0.1 to 20 mass % based on a solid content of the positive resist composition, and a pattern forming method using the same.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a positive resist composition for usein the production process of a semiconductor such as IC, in theproduction of a circuit substrate of liquid crystal, thermal head or thelike, and in the lithography process of other photo-applications, and apattern forming method using the positive resist composition. Morespecifically, the present invention relates to a positive resistcomposition suitable for exposure by an immersion-type projectionexposure apparatus using a light source of emitting far ultravioletlight at a wavelength of 300 nm or less, and a pattern forming methodusing the positive resist composition.

2. Description of the Related Art

Along with the miniaturization of semiconductor devices, the trend ismoving into shorter wavelength of the exposure light source and highernumerical aperture (high NA) of the projection lens. At present, anexposure machine with NA of 0.84 has been developed, where an ArFexcimer laser having a wavelength of 193 nm is used as the light source.As commonly well known, these can be expressed by the followingformulae:(Resolving power)=k ₁·(λ/NA)(Focal depth)=±k ₂ λ/NA ²wherein λ is the wavelength of the exposure light source, NA is thenumerical aperture of the projection lens, and k₁ and k₂ are constantsrelated to the process.

In order to realize still shorter wavelength and higher resolving power,studies are being made on an exposure machine where an F₂ excimer laserhaving a wavelength of 157 nm is used as the light source. However, thelens material used for the exposure apparatus so as to realize shorterwavelength and the material used for the resist are very limited andtherefore, it is extremely difficult to stabilize the production cost orquality of the apparatus and materials. This may lead to a failure inprocuring the exposure apparatus or resist assured of sufficiently highperformance and stability within a required time period.

Conventionally, a so-called immersion method of filling a highrefractive-index liquid (hereinafter sometimes referred to as an“immersion liquid”) between the projection lens and the sample has beenknown as a technique of increasing the resolving power in an opticalmicroscope.

As for the “effect of immersion”, assuming that the wavelength ofexposure light in air is λ₀, the refractive index of the immersionliquid to air is n, the convergence half-angle of beam is θ andNA₀=sinθ, the above-described resolving power and focal depth whenimmersed can be expressed by the following formulae:(Resolving power)=k ₁·(λ₀ /n)/NA ₀(Focal depth)=±k ₂·(λ₀ /n)/NA ₀ ²

That is, the effect of immersion is equal to use of an exposurewavelength of 1/n. In other words, in the case of a projection opticalsystem with the same NA, the focal depth can be made n times larger bythe immersion. This is effective for all pattern profiles and can becombined with super-resolution techniques such as phase-shift method andmodified illumination method which are being studied at present.

Examples of the apparatus where this effect is applied to the transferof a fine image pattern of a semiconductor device are described inJP-A-57-153433 (the term “JP-A” as used herein means an “unexaminedpublished Japanese patent application”) and JP-A-7-220990.

Recent progress of the immersion exposure technique is reported, forexample, in SPIE Proc., 4688, 11 (2002), J. Vac. Sci. Tecnol. B, 17(1999), SPIE Proc., 3999, 2 (2000) and International Publication No.W02004-077158, pamphlet. In the case of using an ArF excimer laser asthe light source, in view of safety on handling as well as transmittanceand refractive index at 193 nm, pure water (refractive index at 193 nm:1.44) is considered to be a most promising immersion liquid. In the caseof using an F₂ excimer laser as the light source, a fluorine-containingsolution is being studied in the light of balance between transmittanceand refractive index at 157 nm, but those satisfied in view ofenvironmental safety or refractive index have been not yet found out.Considering the degree of immersion effect and the maturity of resist,the immersion exposure technique is expected to be most soon mounted onan ArF exposure machine.

Since the discovery of a resist for a KrF excimer laser (248 nm), animage forming method called chemical amplification is used as the imageforming method for a resist so as to compensate the reduction in thesensitivity due to light absorption. The image forming method, forexample, using positive chemical amplification is an image formingmethod where an acid generator in the exposed area decomposes uponexposure to generate an acid, the acid generated is used as a reactioncatalyst in the baking after exposure (PEB: post exposure bake) toconvert the alkali-insoluble group into an alkali-soluble group, and theexposed area is removed by an alkali developer.

A resist for an ArF excimer laser (wavelength: 193 nm) using thischemical amplification mechanism is predominating at present, but moreimprovement is demanded on the profile and pattern collapse.

Also, it is pointed out that when the chemical amplification resist isapplied to immersion exposure, the resist layer comes into contact withthe immersion liquid at the exposure, as a result, the resist layerdeteriorates or a component adversely affecting the immersion liquidbleeds out from the resist layer. International Publication No.W02004-068242, pamphlet describes a case where when the resist for ArFexposure is dipped in water before and after exposure, the resistperformance is changed, and this is indicated as a problem in theimmersion exposure.

Furthermore, in the immersion exposure process, when the exposure isperformed by using a scanning-type immersion exposure machine, unlessthe immersion liquid moves following the movement of lens, the exposurespeed decreases and this may affect the productivity. In the case wherethe immersion liquid is water, the resist film is preferably hydrophobicand ensures good followability of water.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a positive resistcomposition improved in the profile and pattern collapse, and a patternforming method using the positive resist composition. Another object ofthe present invention is to provide a positive resist compositionsuitable for immersion exposure, ensuring that the profile and patterncollapse are not changed at immersion exposure and the followability forwater is good, and a pattern forming method using the positive resistcomposition.

The present invention provides a positive resist composition having thefollowing constructions and a pattern forming method using the positiveresist composition. The above-described objects of the present inventioncan be attained by these composition and method.

(1) A positive resist composition, which comprises:

(A) a resin having a monocyclic or polycyclic alicyclic hydrocarbonstructure, of which solubility in an alkali developer increases under anaction of an acid;

(B) a compound capable of generating an acid upon irradiation withactinic rays or radiation;

(C) a resin having a repeating unit represented by formula (C); and

(D) a solvent,

wherein a content of the resin as the component (C) is from 0.1 to 20mass % based on a solid content of the positive resist composition:

wherein X₁, X₂ and X₃ each independently represents a hydrogen atom, analkyl group or a halogen atom;

L represents a single bond or a divalent linking group; and

Rp₁ represents an acid-decomposable group.

(2) The positive resist composition as described in (1) above,

wherein the resin as the component (C) further has a repeating unitrepresented by formula (C2):

wherein X₄, X₅ and X₆ each independently represents a hydrogen atom, analkyl group or a halogen atom;

L₁ represents a single bond or a divalent linking group; and

Rp₂ represents a non-acid-decomposable group.

(3) The positive resist composition as described in (1) or (2) above,

wherein a content of the resin as the component (C) is from 0.1 to 5mass % based on a solid content of the positive resist composition.

(4) The positive resist composition as described in any of (1) to (3)above,

wherein formula (C) is represented by formula (C1):

wherein X₁, X₂ and X₃ each independently represents a hydrogen atom, analkyl group or a halogen atom; and

R₁₂, R₁₃ and R₁₄ each independently represents an alkyl group, acycloalkyl group, an alkenyl group or an aryl group, or a monovalentgroup formed by bonding at least two of these groups, provided that atleast one of R₁₂, R₁₃ and R₁₄ represents an alkyl group, and two membersout of R₁₂, R₁₃ and R₁₄ may combine to form a ring.

(5) The positive resist composition as described in (4) above,

wherein in formula (C1), R₁₂, R₁₃ and R₁₄ each independently representsan alkyl group or an alkenyl group and at least one of R₁₂, R₁₃ and R₁₄represents an alkyl group.

(6) The positive resist composition as described in any of (1) to (5)above,

wherein the resin as the component (C) comprises a repeating unitrepresented by formula (C1) and a repeating unit represented by formula(C2) in a proportion of from 80 to 100 mol % in total repeating units:

wherein X₁, X₂, X₃, X₄, X₅ and X₆ each independently represents ahydrogen atom, an alkyl group or a halogen atom;

R₁₂, R₁₃ and R₁₄ each independently represents an alkyl group, acycloalkyl group, an alkenyl group or an aryl group, or a monovalentgroup formed by bonding at least two of these groups, provided that atleast one of R₁₂, R₁₃ and R₁₄ represents an alkyl group, and two membersout of R₁₂, R₁₃ and R₁₄ may combine to form a ring;

L₁ represents a single bond or a divalent linking group;

Rp₂ represents a non-acid-decomposable group; and

m and n each represents a molar ratio of the repeating unit, and m=10 to100, n=0 to 90 and m+n=100.

(7) The positive resist composition as described in any of (1) to (5)above,

wherein the resin as the component (C) comprises at least one repeatingunit selected from formulae (C-I) to (C-IV) in a proportion of from 80to 100 mol % in total repeating units, provided that the repeating unitrepresented by formula (C-I) is used in combination with the repeatingunit represented by formula (C-II):

wherein R₁ represents a hydrogen atom or a methyl group;

R₂ represents a hydrocarbon group having two or more —CH₃ partialstructures, provided that when a plurality of R₂'s are present, theplurality of R₂'s may be the same or different;

P₁ represents a single bond, an alkylene group or an ether group, or alinking group having two or more thereof;

P₂ represents a linking group selected from —O—, —NR— and —NHSO₂—,wherein R represents a hydrogen atom or an alkyl group;

x1, x2, y and z represent mol % in total repeating units, and x1represents a number of 0 to 50, x2 represents a number of 0 to 50, yrepresents a number of 0 to 100, z represents a number of 0 to 100,provided that x1, x2, y and z satisfy 80≦x1+x2+y+z≦100; and

n represents an integer of from 1 to 4.

(8) The positive resist composition as described in any of (1) to (7)above,

wherein the resin (A) contains at least a (meth)acrylate-based repeatingunit having a lactone structure and a (meth)acrylate-based repeatingunit having an acid-decomposable group.

(9) The positive resist composition as described in any of (1) to (8)above,

wherein the resin as the component (A) has a repeating unit representedby formula (A1), a repeating unit represented by formula (A2) and arepeating unit represented by formula (A3):

wherein Xa, Xb and Xc each independently represents a hydrogen atom or amethyl group;

R₁ represents a monovalent organic group having a lactone structure;

R₂ represents a monovalent organic group having a hydroxyl group or acyano group; and

R₃ represents a group capable of being detached under an action of anacid.

(10) A pattern forming method, which comprises:

forming a resist film from a positive resist composition as described inany of (1) to (9) above; and

exposing and developing the resist film.

(11) The pattern forming method as described in (10) above,

wherein the exposure is preformed through an immersion liquid.

Furthermore, preferred embodiments of the present invention are setforth below.

(12) The positive resist composition as described in any of(1) to (9)above,

wherein the compound as the component (B) has a triphenylsulfoniumcation structure.

(13) The positive resist composition as described in any of (1) to (9)and (12) above, which further comprises a surfactant.

(14) The positive resist composition as described in any of (1) to (9),(12) and (13) above, which further comprises a basic compound.

(15) The positive resist composition as described in any of (1) to (9)and (12) to (14) above,

wherein the resin (C) has a weight average molecular weight of from3,000 to 15,000 and a dispersity of from 1.2 to 3.0.

(16) The positive resist composition as described in any of (1) to (9)and (12) to (15) above,

wherein the resin (C) does not have a fluorine atom and a silicon atom.

(17) The positive resist composition as described in any of (4) to (9)and (12) to (16) above,

wherein in the resin (C1), R₁₂, R₁₃ and R₁₄ each is an alkyl group, analkenyl group or a cycloalkyl group, or a group formed by bonding atleast two of these groups, and the number of carbon atoms contained inR₁₂ to R₁₄ is from 6 to 20.

(18) The positive resist composition as described in any of (1) to (9)and (12) to (17) above,

wherein the compound (B) is a compound capable of generating a fluorineatom-containing aliphatic sulfonic acid or a fluorine atom-containingbenzenesulfonic acid upon irradiation with actinic rays or radiation.

(19) The positive resist composition as described in any of (1) to (9)and (12) to (18) above,

wherein the entire solid content concentration in the positive resistcomposition is from 1.0 to 6.0 mass %.

(20) The pattern forming method as described in (10) or (11) above,

wherein the exposure is preformed by exposure to light at a wavelengthof from 1 to 200 nm.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view showing a state on evaluating thefollowability of water to a quartz plate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in detail below.

In the present invention, when a group (atomic group) is denoted withoutspecifying whether substituted or unsubstituted, the group includes botha group having no substituent and a group having a substituent. Forexample, an “alkyl group” includes not only an alkyl group having nosubstituent (unsubstituted alkyl group) but also an alkyl group having asubstituent (substituted alkyl group).

[1] (A) Resin Having a Monocyclic or Polycyclic Alicyclic HydrocarbonStructure, of Which Solubility in an Alkali Developer Increases Underthe Action of an Acid

The resin for use in the positive resist composition of the presentinvention is a resin having a monocyclic or polycyclic alicyclichydrocarbon structure, of which solubility in an alkali developerincreases under the action of an acid (acid-decomposable resin), andthis is a resin having a group capable of decomposing under the actionof an acid to produce an alkali-soluble group (hereinafter sometimesreferred to as an “acid-decomposable group”) in the main or side chainor both the main and side chains of the resin (hereinafter sometimesreferred to as an “alicyclic hydrocarbon-based acid-decomposable resin”or a “resin (A)”).

Examples of the alkali-soluble group include groups having a phenolichydroxyl group, a carboxylic acid group, a fluorinated alcohol group, asulfonic acid group, a sulfonamide group, a sulfonylimide group, an(alkylsulfonyl)(alkylcarbonyl)methylene group, an(alkylsulfonyl)(alkylcarbonyl)imide group, a bis(alkylcarbonyl)methylenegroup, a bis(alkylcarbonyl)imide group, a bis(alkylsulfonyl)methylenegroup, a bis(alkylsulfonyl)-imide group, a tris(alkylcarbonyl)methylenegroup or a tris(alkylsulfonyl)methylene group.

Among these alkali-soluble groups, preferred are a carboxylic acidgroup, a fluorinated alcohol group (preferably hexafluoroisopropanol)and a sulfonic acid group.

The acid-decomposable group is preferably a group formed by substitutinga hydrogen atom of such an alkali-soluble group by a group which isdetached under the action of an acid.

Examples of the group which is detached under the action of an acid(hereinafter sometimes referred to as an “acid-detachable group”)include —C(R₃₆)(R₃₇)(R₃₈), —C(R₃₆)(R₃₇)(OR₃₉) and —C(R₀₁)(R₀₂)(OR₃₉). Inthe formulae, R₃₆ to R₃₉ each independently represents an alkyl group, acycloalkyl group, an aryl group, an aralkyl group or an alkenyl group,and R₃₆ and R₃₇ may combine with each other to form a ring. R₀₁ and R₀₂each independently represents a hydrogen atom, an alkyl group, acycloalkyl group, an aryl group, an aralkyl group or an alkenyl group.

Preferred examples of the acid-decomposable group include a cumyl estergroup, an enol ester group, an acetal ester group and a tertiary alkylester group, with a tertiary alkyl ester group being more preferred.

The resin (A) is preferably a resin containing at least one repeatingunit selected from the group consisting of a repeating unit having analicyclic hydrocarbon-containing partial structure represented by anyone of the following formulae (pI) to (pV), and a repeating unitrepresented by the following formula (II-AB).

In formulae (pI) to (pV), R₁₁ represents a methyl group, an ethyl group,an n-propyl group, an isopropyl group, an n-butyl group, an isobutylgroup or a sec-butyl group. Z represents an atomic group necessary forforming a cycloalkyl group together with the carbon atom.

R₁₂ to R₁₆ each independently represents an alkyl group or a cycloalkylgroup, provided that at least one of R₁₂ to R₁₄ or either one of R₁₅ andR₁₆ represents a cycloalkyl group.

R₁₇ to R₂₁ each independently represents a hydrogen atom, an alkyl groupor a cycloalkyl group, provided that at least one of R₁₇ to R₂₁represents a cycloalkyl group and that either one of R₁₉ and R₂₁represents an alkyl group or a cycloalkyl group.

R₂₂ to R₂₅ each independently represents a hydrogen atom, an alkyl groupor a cycloalkyl group, provided that at least one of R₂₂ to R₂₅represents a cycloalkyl group. R₂₃ and R₂₄ may combine with each otherto form a ring.

In formula (II-AB), R₁₁′ and R₁₂′ each independently represents ahydrogen atom, a cyano group, a halogen atom or an alkyl group.

Z′ represents an atomic group for forming an alicyclic structure,containing two bonded carbon atoms (C—C).

Formula (II-AB) is preferably the following formula (II-AB1) or(II-AB2):

In formulae (II-AB1) and (II-AB2), R₁₃′ to R₁₆′ each independentlyrepresents a hydrogen atom, a halogen atom, a cyano group, —COOH,—COOR₅, a group capable of decomposing under the action of an acid,—C(═O)—X-A′-R₁₇′, an alkyl group or a cycloalkyl group, and at least twomembers out of R₁₃′ to R₁₆′ may combine to form a ring.

R₅ represents an alkyl group, a cycloalkyl group or a group having alactone structure.

X represents an oxygen atom, a sulfur atom, —NH—, —NHSO₂— or —NHSO₂NH—.

A′ represents a single bond or a divalent linking group.

R₁₇′ represents —COOH, —COOR₅, —CN, a hydroxyl group, an alkoxy group,—CO—NH—R₆, —CO—NH—SO₂—R₆ or a group having a lactone structure.

R₆ represents an alkyl group or a cycloalkyl group.

n represents 0 or 1.

In formulae (pI) to (pV), the alkyl group of R₁₂ to R₂₅ is preferably alinear or branched alkyl group having a carbon number of 1 to 4, andexamples thereof include a methyl group, an ethyl group, an n-propylgroup, an isopropyl group, an n-butyl group, an isobutyl group and asec-butyl group.

The cycloalkyl group of R₁₂ to R₂₅ and the cycloalkyl group formed by Ztogether with the carbon atom may be monocyclic or polycyclic. Specificexamples thereof include a group having a carbon number of 5 or more andhaving a monocyclo, bicyclo, tricyclo or tetracyclo structure. Thecarbon number thereof is preferably from 6 to 30, more preferably from 7to 25. These cycloalkyl groups each may have a substituent.

Preferred examples of the cycloalkyl group include an adamantyl group, anoradamantyl group, a decalin residue, a tricyclodecanyl group, atetracyclododecanyl group, a norbomyl group, a cedrol group, acyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctylgroup, a cyclodecanyl group and a cyclododecanyl group. Among these,more preferred are an adamantyl group, a norbomyl group, a cyclohexylgroup, a cyclopentyl group, a tetracyclododecanyl group and atricyclodecanyl group.

These alkyl and cycloalkyl groups each may further have a substituent,and examples of the substituent include an alkyl group (having a carbonnumber of 1 to 4), a halogen atom, a hydroxyl group, an alkoxy group(having a carbon number of 1 to 4), a carboxyl group and analkoxycarbonyl group (having a carbon number of 2 to 6). Examples of thesubstituent which these alkyl group, alkoxy group, alkoxycarbonyl groupand the like may further have include a hydroxyl group, a halogen atomand an alkoxy group.

The structures represented by formulae (pI) to (pV) each can be used forthe protection of an alkali-soluble group in the resin.

The repeating unit having an alkali-soluble group protected by thestructure represented by any one of formulae (pI) to (pV) is preferablya repeating unit represented by the following formula (pA):

In formula (pA), R represents a hydrogen atom, a halogen atom or alinear or branched alkyl group having a carbon number of 1 to 4, and aplurality of R's may be the same or different.

A represents a single bond, a sole group selected from the groupconsisting of an alkylene group, an ether group, a thioether group, acarbonyl group, an ester group, an amido group, a sulfonamido group, aurethane group and a urea group, or a combination of two or more groupsselected therefrom. A is preferably a single bond.

Rpa represents any one group of formulae (pI) to (pV).

The repeating unit represented by formula (pA) is most preferably arepeating unit comprising a 2-alkyl-2-adamantyl(meth)acrylate or adialkyl(1-adamantyl)methyl(meth)acrylate.

Specific examples of the repeating unit represented by formula (pA) areset forth below.

In the formulae, Rx represents H, CH₃, CF₃ or CH₂OH, and Rxa and Rxbeach alkyl group having a carbon number of 1 to 4.)

Examples of the halogen atom of R₁₁′ and R₁₂′ in formula (II-AB) includea chlorine atom, a bromine atom, a fluorine atom and an iodine atom.

The alkyl group of R₁₁′ and R₁₂′, includes a linear or branched alkylgroup having a carbon number of 1 to 10.

The atomic group of Z′ for forming an alicyclic structure is an atomicgroup for forming, in the resin, an alicyclic hydrocarbon repeating unitwhich may have a substituent. In particular, an atomic group for forminga crosslinked alicyclic structure to form a crosslinked alicyclichydrocarbon repeating unit is preferred.

Examples of the skeleton of the alicyclic hydrocarbon formed are thesame as those of the cycloalkyl group of R₁₂ to R₂₅ in formulae (pI) to(pVI).

The alicyclic hydrocarbon skeleton may have a substituent, and examplesof the substituent include R₁₃′ to R₁₆′ in formulae (II-AB1) and(II-AB2).

In the alicyclic hydrocarbon-based acid-decomposable resin for use inthe present invention, the group capable of decomposing under the actionof an acid may be contained in at least one repeating unit out of therepeating unit having an alicyclic hydrocarbon-containing partialstructure represented by any one of formulae (pI) to (pV), the repeatingunit represented by formula (II-AB), and the repeating unit comprising acopolymerization component described later.

Various substituents R₁₃′ to R₁₆′ in formulae (II-AB1) and (II-AB2) maywork out to a substituent of an atomic group for forming an alicyclicstructure in formula (II-AB) or an atomic group Z′ for forming acrosslinked alicyclic structure.

Specific examples of the repeating units represented by formulae(II-AB1) and (II-AB2) are set forth below, but the present invention isnot limited to these specific examples.

The alicyclic hydrocarbon-based acid-decomposable resin for use in thepresent invention preferably contains a group having a lactone ring. Asfor the group having a lactone ring, any group may be used as long as ithas a lactone ring, but a group having a 5- to 7-membered ring lactonestructure is preferred. The 5- to 7-membered ring lactone structure ispreferably condensed with another ring structure in the form of forminga bicyclo or spiro structure. A group having a lactone structurerepresented by any one of the following formulae (LC1-1) to (LC1-16) ismore preferred. The group having a lactone structure may be bondeddirectly to the main chain. Among these lactone structures, preferredare (LC1-1), (LC1-4), (LC1-5), (LC1-6), (LC1-13) and (LC1-14). By virtueof using a lactone structure, the line edge roughness and developmentdefect are improved.

The lactone structure moiety may or may not have a substituent (Rb₂).Preferred examples of the substituent (Rb₂) include an alkyl grouphaving a carbon number of 1 to 8, a cycloalkyl group having a carbonnumber of 4 to 7, an alkoxy group having a carbon number of 1 to 8, analkoxycarbonyl group having a carbon number of 1 to 8, a carboxyl group,a halogen atom, a hydroxyl group, a cyano group and an acid-decomposablegroup. n₂ represents an integer of 0 to 4. When n₂ is an integer of 2 ormore, the plurality Of Rb₂'s may be the same or different and also, theplurality of Rb₂'s may combine with each other to form a ring.

Examples of the repeating unit having a lactone structure represented byany one of formulae (LC1-1) to (LC1-13) include a repeating unit whereat least one of R₁₃′ to R₁₆′ in formula (II-AB1) or (II-AB2) has a grouprepresented by any one of formulae (LC1-1) to (LC1-16) (for example, R₅of —COOR₅ is a group represented by any one of formulae (LC1-1) to(LC1-16)), and a repeating unit represented by the following formula(AI):

In formula (AI), Rb₀ represents a hydrogen atom, a halogen atom or analkyl group having a carbon number of 1 to 4.

Preferred examples of the substituent which the alkyl group of Rb₀ mayhave include a hydroxyl group and a halogen atom.

Examples of the halogen atom of Rb₀ include a fluorine atom, a chlorineatom, a bromine atom and an iodine atom.

Rb₀ is preferably a hydrogen atom or a methyl group.

Ab represents an alkylene group, a divalent linking group having amonocyclic or polycyclic alicyclic hydrocarbon structure, a single bond,an ether group, an ester group, a carbonyl group, a carboxyl group, or adivalent group comprising a combination thereof, preferably a singlebond or a linking group represented by -Ab₁-CO₂—. Ab₁ is a linear orbranched alkylene group or a monocyclic or polycyclic cycloalkylenegroup, preferably a methylene group, an ethylene group, a cyclohexylgroup, an adamantyl group or a norbomyl group.

V represents a group having a lactone structure represented by any oneof formulae (LC1-1) to (LC1-16).

The repeating unit having a lactone structure usually has an opticalisomer, but any optical isomer may be used. One optical isomer may beused alone or a mixture of a plurality of optical isomers may be used.In the case of mainly using one optical isomer, the optical purity (ee)thereof is preferably 90 or more, more preferably 95 or more.

Specific examples of the repeating unit having a lactonestructure-containing group are set forth below, but the presentinvention is not limited thereto.

(In the formulae, Rx is H, CH₃, CH₂OH or CF₃.)

(In the formulae, Rx is H, CH₃, CH₂OH or CF₃.)

(In the formulae, Rx is H, CH₃, CH₂OH or CF₃.)

The alicyclic hydrocarbon-based acid-decomposable resin for use in thepresent invention preferably contains a repeating unit having analicyclic hydrocarbon structure substituted by a polar group. By virtueof this repeating unit, the adhesion to substrate and the affinity fordeveloper are enhanced. The alicyclic hydrocarbon structure of thealicyclic hydrocarbon structure substituted by a polar group ispreferably an adamantyl group, a diamantyl group or a norbomane group.The polar group is preferably a hydroxyl group or a cyano group. Thealicyclic hydrocarbon structure substituted by a polar group ispreferably a partial structure represented by any one of the followingformulae (VIIa) to (VIId):

In formulae (VIIa) to (VIIc), R_(2c) to R_(4c) each independentlyrepresents a hydrogen atom, a hydroxyl group or a cyano group, providedthat at least one of R_(2c) to R_(4c) represents a hydroxyl group or acyano group. A structure where one or two member(s) out of R_(2c) toR_(4c) is(are) a hydroxyl group with the remaining being a hydrogen atomis preferred. In formula (VIIa), it is more preferred that two membersout of R_(2c) to R_(4c) are a hydroxyl group and the remaining is ahydrogen atom.

Examples of the repeating unit having a partial structure represented byany one of formulae (VIIa) to (VIId) include a repeating unit where atleast one of R₁₃′ to R₁₆′ in formula (II-AB1) or (II-AB2) is a partialstructure represented by any one of formulae (VIIa) to (VIId) (forexample, R₅ of —COOR₅ is a partial structure represented by any one offormulae (VIIa) to (VIId)), and repeating units represented by thefollowing formulae (AIIa) to (AIId):

In formulae (AIIa) to (AIId), R_(1c) represents a hydrogen atom, amethyl group, a trifluoromethyl group or a hydroxymethyl group.

Specific examples of the repeating unit having a partial structurerepresented by any one of formulae (VIIa) to (VIId) are set forth below,but the present invention is not limited thereto.

The alicyclic hydrocarbon-based acid-decomposable resin for use in thepresent invention may contain a repeating unit represented by thefollowing formula (VIII):

In formula (VIII), Z₂ represents —O— or —N(R₄₁)—. R₄₁ represents ahydrogen atom, a hydroxyl group, an alkyl group or —OSO₂—R₄₂. R₄₂represents an alkyl group, a cycloalkyl group or a camphor residue. Thealkyl group of R₄₁, and R₄₂ may be substituted by a halogen atom(preferably fluorine atom) or the like.

Specific examples of the repeating unit represented by formula (VIII)are set forth below, but the present invention is not limited thereto.

The alicyclic hydrocarbon-based acid-decomposable resin for use in thepresent invention preferably contains a repeating unit having analkali-soluble group, more preferably a repeating unit having a carboxylgroup. By virtue of containing such a repeating unit, the resolutionincreases in the usage of forming contact holes. As for the repeatingunit having a carboxyl group, both a repeating unit where a carboxylgroup is directly bonded to the resin main chain, such as repeating unitby an acrylic acid or a methacrylic acid, and a repeating unit where acarboxyl group is bonded to the resin main chain through a linkinggroup, are preferred. The linking group may have a monocyclic orpolycyclic hydrocarbon structure. An acrylic acid and a methacrylic acidare most preferred.

The alicyclic hydrocarbon-based acid-decomposable resin for use in thepresent invention may further contain a repeating unit having from 1 to3 groups represented by formula (F1). By virtue of this repeating unit,the line edge roughness performance is enhanced.

In formula (F1), R₅₀ to R₅₅ each independently represents a hydrogenatom, a fluorine atom or an alkyl group, provided that at least one ofR₅₀ to R₅₅ is a fluorine atom or an alkyl group with at least onehydrogen atom being substituted by a fluorine atom.

Rxa represents a hydrogen atom or an organic group (preferably anacid-detachable group, an alkyl group, a cycloalkyl group, an acyl groupor an alkoxycarbonyl group).

The alkyl group of R₅₀ to R₅₅ may be substituted by a halogen atom(e.g., fluorine), a cyano group or the like, and the alkyl group ispreferably an alkyl group having a carbon number of 1 to 3, such asmethyl group and trifluoromethyl group. It is preferred that R₅₀ to R₅₅all are a fluorine atom.

The organic group represented by Rxa is preferably an acid-detachablegroup or an alkyl, cycloalkyl, acyl, alkylcarbonyl, alkoxycarbonyl,alkoxycarbonylmethyl, alkoxymethyl or 1-alkoxyethyl group which may havea substituent.

The repeating unit having a group represented by formula (F1) ispreferably a repeating unit represented by the following formula (F2):

In formula (F2), Rx represents a hydrogen atom, a halogen atom or analkyl group having a carbon number of 1 to 4. Preferred examples of thesubstituent which the alkyl group of Rx may have include a hydroxylgroup and a halogen atom.

Fa represents a single bond or a linear or branched alkylene group,preferably a single bond.

Fb represents a monocyclic or polycyclic hydrocarbon group.

Fc represents a single bond or a linear or branched alkylene group,preferably a single bond or a methylene group.

F₁ represents a group represented by formula (F1).

p₁ represents a number of 1 to 3.

The cyclic hydrocarbon group in Fb is preferably a cyclopentyl group, acyclohexyl group or a norbornyl group.

Specific examples of the repeating unit having a structure of formula(F1) are set forth below.

The alicyclic hydrocarbon-based acid-decomposable resin for use in thepresent invention may contain, in addition to the above-describedrepeating units, various repeating structural units for the purpose ofcontrolling dry etching resistance, suitability for standard developer,adhesion to substrate, resist profile and properties generally requiredof the resist, such as resolving power, heat resistance and sensitivity.

Examples of such a repeating structural unit include, but are notlimited to, repeating structural units corresponding to the monomersdescribed below.

By virtue of such a repeating structural unit, the performance requiredof the alicyclic hydrocarbon-based acid-decomposable resin,particularly, (1) solubility in the coating solvent, (2) film-formingproperty (glass transition point), (3) alkali developability, (4) filmloss (selection of hydrophilic, hydrophobic or alkali-soluble group),(5) adhesion of unexposed area to substrate, (6) dry etching resistance,and the like can be subtly controlled.

Examples of the monomer include a compound having oneaddition-polymerizable unsaturated bond selected from acrylic acidesters, methacrylic acid esters, acrylamides, methacrylamides, allylcompounds, vinyl ethers and vinyl esters.

Other than these, an addition-polymerizable unsaturated compoundcopolymerizable with the monomers corresponding to the above-describedvarious repeating structural units may be copolymerized.

In the alicyclic hydrocarbon-based acid-decomposable resin, the molarratio of respective repeating structural units contained isappropriately determined to control the dry etching resistance ofresist, suitability for standard developer, adhesion to substrate,resist profile and performances generally required of the resist, suchas resolving power, heat resistance and sensitivity.

The preferred embodiment of the alicyclic hydrocarbon-basedacid-decomposable resin for use in the present invention includes thefollowings:

(1) a resin containing a repeating unit having an alicyclichydrocarbon-containing partial structure represented by any one offormulae (pI) to (pV) (side chain type), preferably containing a(meth)acrylate repeating unit having a structure represented by any oneof formulae (pI) to (pV), and

(2) a resin containing a repeating unit represented by formula (II-AB)(main chain type).

The embodiment of (2) further includes:

(3) a resin having a repeating unit represented by formula (II-AB), amaleic anhydride derivative and a (meth)acrylate structure (hybridtype).

In the alicyclic hydrocarbon-based acid-decomposable resin, the contentof the repeating unit having an acid-decomposable group is preferablyfrom 10 to 60 mol %, more preferably from 20 to 50 mol %, still morepreferably from 25 to 40 mol %, based on all repeating structural units.

In the alicyclic hydrocarbon-based acid-decomposable resin, the contentof the repeating unit having an alicyclic hydrocarbon-containing partialstructure represented by any one of formulae (pI) to (pV) is preferablyfrom 20 to 70 mol %, more preferably from 20 to 50 mol %, still morepreferably from 25 to 40 mol %, based on all repeating structural units.

In the alicyclic hydrocarbon-based acid-decomposable resin, the contentof the repeating unit represented by formula (II-AB) is preferably from10 to 60 mol %, more preferably from 15 to 55 mol %, still morepreferably from 20 to 50 mol %, based on all repeating structural units.

As for the repeating structural unit based on the monomer which is thefurther copolymerization component described above, the content thereofin the resin may also be appropriately determined according to thedesired resist performance but in general, the content is preferably 99mol % or less, more preferably 90 mol % or less, still more preferably80 mol % or less, based on the total molar number of the repeatingstructural unit having an alicyclic hydrocarbon-containing partialstructure represented by any one of formulae (pI) to (pV) and therepeating unit represented by formula (II-AB).

In the case of using the composition of the present invention forexposure with ArF, the resin preferably has no aromatic group in view oftransparency to ArF light.

The alicyclic hydrocarbon-based acid-decomposable resin preferably has arepeating unit represented by the following formula (A1), a repeatingunit represented by the following formula (A2) and a repeating unitrepresented by the following formula (A3):

In formulae (A1) to (A3), Xa, Xb and Xc each independently represents ahydrogen atom or a methyl group.

R₁ represents a monovalent organic group having a lactone structure.

R₂ represents a monovalent organic group having a hydroxyl group or acyano group.

R₃ represents a group which is detached under the action of an acid.

The repeating unit represented by formula (A1) is preferably a repeatingunit represented by formula (A1).

The proportion of the repeating unit represented by formula (A1) ispreferably from 25 to 50 mol % based on all repeating units in thealicyclic hydrocarbon-based acid-decomposable resin.

The repeating unit represented by formula (A2) is preferably a repeatingunit represented by formula (AIIa) or (AIIb).

The proportion of the repeating unit represented by formula (A2) ispreferably from 5 to 30 mol % based on all repeating units in thealicyclic hydrocarbon-based acid-decomposable resin.

The repeating unit represented by formula (A3) is preferably a repeatingunit represented by formula (pA).

The proportion of the repeating unit represented by formula (A3) ispreferably from 25 to 50 mol % based on all repeating units in thealicyclic hydrocarbon-based acid-decomposable resin.

The alicyclic hydrocarbon-based acid-decomposable resin for use in thepresent invention is preferably a resin where all repeating units arecomposed of a repeating unit by a (meth)acrylate. In this case, any of aresin where the repeating units all are a repeating unit by amethacrylate, a resin where the repeating units all are a repeating unitby an acrylate, and a resin where the repeating units are a repeatingunit by a methacrylate/acrylate mixture may be used, but the content ofthe repeating unit by an acrylate is preferably 50 mol % or less basedon all repeating units. The alicyclic hydrocarbon-basedacid-decomposable resin is more preferably a ternary copolymerizationpolymer comprising from 20 to 50 mol % of the repeating unit having analicyclic hydrocarbon-containing partial structure represented by anyone of formulae (pI) to (pV), from 20 to 50 mol % of the repeating unithaving a lactone structure and from 5 to 30 mol % of the repeating unithaving an alicyclic hydrocarbon structure substituted by a polar group,or a quaternary copolymerization polymer further comprising from 0 to 20mol % of other repeating units.

In particular, the resin is preferably a ternary copolymerizationpolymer comprising from 20 to 50 mol % of the repeating unit having anacid-decomposable group represented by any one of the following formulae(ARA-1) to (ARA-5), from 20 to 50 mol % of the repeating unit having alactone group represented by any one of the following formulae (ARL-1)to (ARL-6), and from 5 to 30 mol % of the repeating unit having analicyclic hydrocarbon structure substituted by a polar group representedby any one of the following formulae (ARH-1) to (ARH-3), or a quaternarycopolymerization polymer further comprising from 5 to 20 mol % of therepeating unit containing a carboxyl group or a structure represented byformula (F1), or the repeating unit having an alicyclic hydrocarbonstructure and not exhibiting acid decomposability.

(In the formulae, Rxy₁ represents a hydrogen atom or a methyl group, andRxa₁ and Rxb₁ each independently represents a methyl group or an ethylgroup).

The weight average molecular weight of the alicyclic hydrocarbon-basedacid-decomposable resin for use in the present invention is preferablyfrom 1,500 to 100,000, more preferably from 2,000 to 70,000, still morepreferably from 3,000 to 50,000. The dispersity (Mw/Mn) of the alicyclichydrocarbon-based acid-decomposable resin for use in the presentinvention is preferably from 1.0 to 3.0, more preferably from 1.2 to2.5, still more preferably from 1.2 to 1.6.

In view of compatibility with the resin (C), the alicyclichydrocarbon-based acid-decomposable resin of the present inventionpreferably contains no fluorine atom and no silicon atom.

The alicyclic hydrocarbon-based acid-decomposable resin for use in thepresent invention can be synthesized by an ordinary method (for example,radical polymerization). Examples of the synthesis method in generalinclude a batch polymerization method of dissolving monomer species andan initiator in a solvent and heating the solution, thereby effectingthe polymerization, and a dropping polymerization method of addingdropwise a solution containing monomer species and an initiator to aheated solvent over 1 to 10 hours. A dropping polymerization method ispreferred. Examples of the reaction solvent include tetrahydrofuran,1,4-dioxane, ethers (e.g., diisopropyl ether), ketones (e.g., methylethyl ketone, methyl isobutyl ketone), an ester solvent (e.g., ethylacetate), an amide solvent (e.g., dimethylformamide, diethylacetamide),and a solvent capable of dissolving the composition of the presentinvention, which is described later, such as propylene glycol monomethylether acetate, propylene glycol monomethyl ether and cyclohexanone. Thepolymerization is preferably performed by using the same solvent as thesolvent used in the resist composition of the present invention. By theuse of this solvent, generation of particles during storage can besuppressed.

The polymerization reaction is preferably performed in an inert gasatmosphere such as nitrogen and argon. As for the polymerizationinitiator, the polymerization is started by using a commerciallyavailable radical initiator (e.g., azo-based initiator, peroxide). Theradical initiator is preferably an azo-based initiator, and an azo-basedinitiator having an ester group, a cyano group or a carboxyl group ispreferred. Preferred examples of the initiator includeazobisisobutyronitrile, azobisdimethylvaleronitrile and dimethyl2,2′-azobis(2-methyl-propionate). The initiator is added additionally orin parts, if desired. After the completion of reaction, the reactant ischarged into a solvent, and the desired polymer is recovered by a methodsuch as powder or solid recovery. The reaction concentration is from 5to 50 mass %, preferably from 10 to 30 mass %, and the reactiontemperature is usually from 10 to 150° C., preferably from 30 to 120°C., more preferably from 50 to 100° C. (In this specification, massratio is equal to weight ratio.)

In the present invention, the amount of the resin (A) added in thephotosensitive composition is from 50 to 99.7 mass %, preferably from 70to 99.5 mass %, based on the entire solid content. In addition to theabove-described resin for use in the present invention, other resins mayalso be used, if desired. In the composition of the present invention,the other resin may be mixed at a ratio of preferably 70 parts by massor less, more preferably 50 parts by mass or less, per 100 parts by massof the resin (A) for use in the present invention.

[2] (B) Compound Capable of Generating an Acid Upon Irradiation withActinic Rays or Radiation

The positive resist composition of the present invention comprises acompound capable of generating an acid upon irradiation with actinicrays or radiation (hereinafter sometimes referred to as an “acidgenerator”).

The acid generator may be appropriately selected from a photoinitiatorfor photocationic polymerization, a photoinitiator for photoradicalpolymerization, a photo-decoloring agent for coloring matters, aphoto-discoloring agent, a known compound capable of generating an acidupon irradiation with actinic rays or radiation, which is used formicroresist or the like, and a mixture thereof.

Examples thereof include a diazonium salt, a phosphonium salt, asulfonium salt, an iodonium salt, an imidosulfonate, an oxime sulfonate,a diazodisulfone, a disulfone and an o-nitrobenzyl sulfonate.

Also, a compound where such a group or compound capable of generating anacid upon irradiation with actinic rays or radiation is introduced intothe main or side chain of the polymer, for example, compounds describedin U.S. Pat. No. 3,849,137, German Patent 3,914,407, JP-A-63-26653,JP-A-55-164824, JP-A-62-69263, JP-A-63-146038, JP-A-63-163452,JP-A-62-153853 and JP-A-63-146029, may be used.

Furthermore, compounds capable of generating an acid by the effect oflight described, for example, in U.S. Pat. No. 3,779,778 and EuropeanPatent 126,712 may also be used.

Out of the compounds capable of decomposing upon irradiation withactinic rays or radiation to generate an acid, preferred compoundsinclude compounds represented by the following formulae (ZI), (ZII) and(ZIII):

In formula (ZI), R₂₀₁, R₂₀₂ and R₂₀₃ each independently represents anorganic group.

X⁻ represents a non-nucleophilic anion, and preferred examples thereofinclude sulfonate anion, carboxylate anion, bis(alkylsulfonyl)amideanion, tris(alkylsulfonyl)methide anion, BF₄ ⁻, PF₆ ⁻ and SbF₆ ⁻. Theanion is preferably an organic anion containing a carbon atom.

The preferred organic anion includes the organic anions represented bythe following formulae:

In the formulae, Rc₁ represents an organic group.

The organic group of Rc₁ includes an organic group having a carbonnumber of 1 to 30, and preferred examples thereof include an alkylgroup, an aryl group, and a group where a plurality of such groups areconnected through a single bond or a linking group such as —O—, —CO₂—,—S—, —SO₃— and —SO₂N(Rd₁)—. Rd₁ represents a hydrogen atom or an alkylgroup.

Rc₃, Rc₄ and RC₅ each independently represents an organic group.Preferred organic groups of Rc₃, Rc₄ and Rc₅ are the same as thepreferred organic groups in Rb₁. In particular, the organic group ispreferably a perfluoroalkyl group having a carbon number of 1 to 4.

Rc₃ and Rc₄ may combine to form a ring. The group formed by combiningRc₃ and Rc₄ includes an alkylene group and an arylene group, and aperfluoroalkylene group having a carbon number of 2 to 4 is preferred.

The organic group of Rc₁ and Rc₃ to Rc₅ is in particular preferably analkyl group with the 1-position being substituted by a fluorine atom ora fluoroalkyl group, or a phenyl group substituted by a fluorine atom ora fluoroalkyl group. By virtue of having a fluorine atom or afluoroalkyl group, the acidity of the acid generated upon irradiationwith light increases and the sensitivity is enhanced. Also, when Rc₃ andRc₄ are combined to form a ring, the acidity of the acid generated uponirradiation with light increases and the sensitivity is enhanced.

The carbon number of the organic group as R₂₀₁, R₂₀₂ and R₂₀₃ in formula(ZI) is generally from 1 to 30, preferably from 1 to 20.

Two members out of R₂₀₁ to R₂₀₃ may combine to form a ring structure,and the ring may contain an oxygen atom, a sulfur atom, an ester bond,an amide bond or a carbonyl group. Examples of the group formed bycombining two members out of R₂₀₁ to R₂₀₃ include an alkylene group(e.g., butylene, pentylene).

Specific examples of the organic group as R₂₀₁, R₂₀₂ and R₂₀₃ includecorresponding groups in the compounds (ZI-1), (ZI-2) and (ZI-3) whichare described later.

The compound may be a compound having a plurality of structuresrepresented by formula (ZI). For example, the compound may be a compoundhaving a structure that at least one of R₂₀₁ to R₂₀₃ in the compoundrepresented by formula (ZI) is bonded to at least one of R₂₀, to R₂₀₃ inanother compound represented by formula (ZI).

The component (ZI) is more preferably a compound (ZI-1), (ZI-2) or(ZI-3) described below.

The compound (ZI-1) is an arylsulfonium compound where at least one ofR₂₀₁ to R₂₀₃ in formula (Z1) is an aryl group, that is, a compoundhaving an arylsulfonium as the cation.

In the arylsulfonium compound, R₂₀₁ to R₂₀₃ all may be an aryl group ora part of R₂₀₁ to R₂₀₃ may be an aryl group with the remaining being analkyl group or a cycloalkyl group.

Examples of the arylsulfonium compound include a triarylsulfoniumcompound, a diarylalkylsulfonium compound, an aryldialkylsulfoniumcompound, a diarylcycloalkyl-sulfonium compound and anaryldicycloalkylsulfonium compound.

The aryl group in the arylsulfonium compound is preferably an aryl groupsuch as phenyl group and naphthyl group, or a heteroaryl group such asindole residue and pyrrole residue, more preferably a phenyl group or anindole residue. In the case where the arylsulfonium compound has two ormore aryl groups, these two or more aryl groups may be the same ofdifferent.

The alkyl group which is present, if desired, in the arylsulfoniumcompound is preferably a linear or branched alkyl group having a carbonnumber of 1 to 15, and examples thereof include a methyl group, an ethylgroup, a propyl group, an n-butyl group, a sec-butyl group and atert-butyl group.

The cycloalkyl group which is present, if desired, in the arylsulfoniumcompound is preferably a cycloalkyl group having a carbon number of 3 to15, and examples thereof include a cyclopropyl group, a cyclobutyl groupand a cyclohexyl group.

The aryl group, alkyl group and cycloalkyl group of R₂₀₁ to R₂₀₃ eachmay have, as the substituent, an alkyl group (for example, an alkylgroup having a carbon number of 1 to 15), a cycloalkyl group (forexample, a cycloalkyl group having a carbon number of 3 to 15), an arylgroup (for example, an aryl group having a carbon number of 6 to 14), analkoxy group (for example, an alkoxy group having a carbon number of 1to 15), a halogen atom, a hydroxyl group or a phenylthio group. Thesubstituent is preferably a linear or branched alkyl group having acarbon number of 1 to 12, a cycloalkyl group having a carbon number of 3to 12, or a linear, branched or cyclic alkoxy group having a carbonnumber of 1 to 12, and more preferably an alkyl group having a carbonnumber of 1 to 4 or an alkoxy group having a carbon number of 1 to 4.The substituent may be substituted to any one of three members R₂₀₁ toR₂₀₃ or may be substituted to all of these three members. In the casewhere R₂₀I to R₂₀₃ are an aryl group, the substituent is preferablysubstituted at the p-position of the aryl group.

The compound (ZI-2) is described below.

The compound (ZI-2) is a compound where R₂₀₁ to R₂₀₃ in formula (ZI)each independently represents an aromatic ring-free organic group. Thearomatic ring as used herein includes an aromatic ring containing aheteroatom.

The aromatic ring-free organic group as R₂₀₁ to R₂₀₃ generally has acarbon number of 1 to 30, preferably from 1 to 20.

R₂₀₁ to R₂₀₃ each is independently preferably an alkyl group, acycloalkyl group, an allyl group or a vinyl group, more preferably alinear, branched or cyclic 2-oxoalkyl group or an alkoxycarbonylmethylgroup, still more preferably a linear or branched 2-oxoalkyl group.

The alkyl group as R₂₀₁ to R₂₀₃ may be either linear or branched and ispreferably a linear or branched alkyl group having a carbon number of 1to 10, and examples thereof include a methyl group, an ethyl group, apropyl group, a butyl group and a pentyl group. The alkyl group as R₂₀₁to R₂₀₃ is more preferably a linear or branched 2-oxoalkyl group or analkoxycarbonylmethyl group.

The cycloalkyl group as R₂₀₁ to R₂₀₃ is preferably a cycloalkyl grouphaving a carbon number of 3 to 10, and examples thereof include acyclopentyl group, a cyclohexyl group and a norbomyl group. Thecycloalkyl group as R₂₀₁ to R₂₀₃ is more preferably a cyclic 2-oxoalkylgroup.

The linear, branched or cyclic 2-oxoalkyl group as R₂₀₁ to R₂₀₃ ispreferably a group having >C═O at the 2-position of the above-describedalkyl or cycloalkyl group.

The alkoxy group in the alkoxycarbonylmethyl group as R₂₀₁ to R₂₀₃ ispreferably an alkoxy group having a carbon number of 1 to 5, andexamples thereof include a methoxy group, an ethoxy group, a propoxygroup, a butoxy group and a pentoxy group.

R₂₀₁ to R₂₀₃ each may be further substituted by a halogen atom, analkoxy group (for example, an alkoxy group having a carbon number of 1to 5), a hydroxyl group, a cyano group or a nitro group.

The compound (ZI-3) is a compound represented by the following formula(ZI-3), and this is a compound having a phenacylsulfonium saltstructure.

In formula (ZI-3), R_(1c) to R_(5c) each independently represents ahydrogen atom, an alkyl group, a cycloalkyl group, an alkoxy group or ahalogen atom.

R_(6c) and R_(7c) each represents a hydrogen atom, an alkyl group or acycloalkyl group.

R_(x) and R_(y) each independently represents an alkyl group, acycloalkyl group, an allyl group or a vinyl group.

Any two or more members out of R_(1c) to R_(7c) or a pair of R_(x) andR_(y) may combine with each other to form a ring structure. The ringstructure may contain an oxygen atom, a sulfur atom, an ester bond or anamide bond. Examples of the group formed by combining any two or moremembers out of R_(1c) to R_(7c) or a pair of R_(x) and R_(y) include abutylene group and a pentylene group.

X⁻ represents a non-nucleophilic anion, and examples thereof are thesame as those of the non-nucleophilic anion of X⁻ in formula (I).

The alkyl group as R_(1c) to R_(7c) may be either linear or branched andis preferably a linear or branched alkyl group having a carbon number of1 to 20, more preferably a linear or branched alkyl group having acarbon number of 1 to 12, and examples thereof include a methyl group,an ethyl group, a linear or branched propyl group, a linear or branchedbutyl group, and a linear or branched pentyl group.

The cycloalkyl group as R_(1c) to R_(7c) is preferably a cycloalkylgroup having a carbon number of 3 to 20, more preferably a cycloalkylgroup having a carbon number of 3 to 8, and examples thereof include acyclopentyl group and a cyclohexyl group.

The alkoxy group as R_(1c) to R_(5c) may be linear, branched or cyclicand this is, for example, an alkoxy group having a carbon number of 1 to10, preferably a linear or branched alkoxy group having a carbon numberof 1 to 5 (for example, a methoxy group, an ethoxy group, a linear orbranched propoxy group, a linear or branched butoxy group, and a linearor branched pentoxy group) or a cyclic alkoxy group having a carbonnumber of 3 to 8 (e.g., cyclopentyloxy, cyclohexyloxy).

A compound where any one of R_(1c) to R_(5c) is a linear or branchedalkyl group, a cycloalkyl group or a linear, branched or cyclic alkoxygroup is preferred, and a compound where the sum of carbon numbers ofR_(1c) to R_(5c) is from 2 to 15 is more preferred. In this case, thesolubility in a solvent is more enhanced, and production of particlesduring storage can be suppressed.

The alkyl group of R_(x) and R_(y) is the same as the alkyl group ofR_(1c) to R_(7c). The alkyl group as R_(x) and R_(y) is more preferablya linear or branched 2-oxoalkyl group or an alkoxycarbonylmethyl group.

The cycloalkyl group of R_(x) and R_(y) is the same as the cycloalkylgroup of R_(1c) to R_(7c). The cycloalkyl group as R_(x) and R_(y) ismore preferably a cyclic 2-oxoalkyl group.

The linear, branched or cyclic 2-oxoalkyl group includes a grouphaving >C═O at the 2-position of the alkyl group or cycloalkyl group asR_(1c) to R_(7c).

The alkoxy group in the alkoxycarbonylmethyl group is the same as thealkoxy group of R_(1c) to R_(5c).

R_(x) and R_(y) each is preferably an alkyl group having a carbon numberof 4 or more, more preferably 6 or more, still more preferably 8 ormore.

In formulae (ZII) and (ZIII), R₂₀₄ to R₂₀₇ each independently representsan aryl group, an alkyl group or a cycloalkyl group.

The aryl group of R₂₀₄ to R₂₀₇ is preferably a phenyl group or anaphthyl group, more preferably a phenyl group.

The alkyl group of R₂₀₄ to R₂₀₇ may be linear or branched and ispreferably a linear or branched alkyl group having a carbon number of 1to 10, and examples thereof include a methyl group, an ethyl group, apropyl group, a butyl group and a pentyl group.

The cycloalkyl group of R₂₀₄ to R₂₀₇ is preferably a cycloalkyl grouphaving a carbon number of 3 to 10, and examples thereof include acyclopentyl group, a cyclohexyl group and a norbomyl group.

R₂₀₄ to R₂₀₇ each may have a substituent. Examples of the substituentwhich R₂₀₄ to R₂₀₇ each may have include an alkyl group (for example, analkyl group having a carbon number of 1 to 15), an aryl group (forexample, an aryl group having a carbon number of 6 to 15), an alkoxygroup (for example, an alkoxy group having a carbon number of 1 to 15),a halogen atom, a hydroxyl group and a phenylthio group.

X⁻ represents a non-nucleophilic anion, and examples thereof are thesame as those of the non-nucleophilic anion of X⁻ in formula (I).

Out of the compounds capable of decomposing upon irradiation withactinic rays or radiation to generate an acid, preferred compoundsfurther include the compounds represented by the following formulae(ZIV), (ZV) and (ZVI):

In formulae (ZIV) to (ZVI), Ar₃ and Ar₄ each independently represents anaryl group.

R₂₀₆ represents an alkyl group, a cycloalkyl group or an aryl group.

R₂₀₇ and R₂₀₈ each independently represents an alkyl group, a cycloalkylgroup, an aryl group or an electron-withdrawing group. R₂₀₇ ispreferably an aryl group, and R₂₀₈ is preferably an electron-withdrawinggroup, more preferably a cyano group or a fluoroalkyl group.

A represents an alkylene group, an alkenylene group or an arylene group.

Among the compounds capable of decomposing upon irradiation with actinicrays or radiation to generate an acid, more preferred are compoundsrepresented by formulae (ZI) to (ZIII).

The compound capable of generating an acid upon irradiation with actinicrays or radiation is more preferably a compound having atriphenylsulfonium cation structure.

Particularly preferred examples of the compound capable of decomposingupon irradiation with actinic rays or radiation to generate an acid areset forth below.

One acid generator may be used alone, or two or more kinds of acidgenerators may be used in combination. In the case of using two or morekinds of acid generators in combination, compounds capable of generatingtwo kinds of organic acids differing in the total atom number except forhydrogen atom by 2,or more are preferably combined.

The content of the acid generator in the composition is preferably from0.1 to 20 mass %, more preferably from 0.5 to 10 mass %, still morepreferably from 1 to 7 mass %, based on the entire solid content of theresist composition.

[3] (C) Resin Having a Repeating Unit Represented by Formula (C)

The positive resist composition of the present invention comprises aresin having a repeating unit represented by the following formula (C):

In formula (C), X₁, X₂ and X₃ each independently represents a hydrogenatom, an alkyl group or a halogen atom.

L represents a single bond or a divalent linking group.

Rp₁ represents an acid-decomposable group.

The alkyl group of X₁, X₂ and X₃ in formula (C) is preferably a linearor branched alkyl group having a carbon number of 1 to 5, and examplesthereof include a methyl group, an ethyl group, an n-propyl group, anisopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group,a pentyl group, an isopentyl group, a neopentyl group and a tert-pentylgroup.

The divalent linking group of L is preferably, for example, a soledivalent linking group selected from the group consisting of an alkylenegroup, a cycloalkylene group, an ether group, a thioether group, acarbonyl group, an ester group, an amido group, a sulfonamido group, aurethane group and a urea group, or a divalent linking group comprisinga combination of two or more groups selected therefrom.

The acid-decomposable group of Rp₁ is, for example, an alkali-solublegroup such as carboxyl group and phenolic hydroxyl group, preferably agroup where the hydrogen atom of a carboxyl group is protected by agroup which is detached under the action of an acid.

Examples of the group which is detached under the action of an acidinclude —C(R₃₆)(R₃₇)(R₃₈), —C(R₃₆)(R₃₇)(OR₃₉) and —C(R₀₁)(R₀₂)(OR₃₉).

In the formulae, R₃₆ to R₃₉ each independently represents an alkylgroup, a cycloalkyl group, an aryl group, an aralkyl group or an alkenylgroup, and R₃₆ and R₃₇ may combine with each other to form a ring.

R₀₁ and R₀₂ each independently represents a hydrogen atom, an alkylgroup, a cycloalkyl group, an aryl group, an aralkyl group or an alkenylgroup.

The alkyl group of R₃₆ to R₃₉, R₀₁ and R₀₂ is preferably an alkyl grouphaving a carbon number of 1 to 8, and examples thereof include a methylgroup, an ethyl group, a propyl group, an n-butyl group, a sec-butylgroup, a hexyl group and an octyl group.

The cycloalkyl group of R₃₆ to R₃₉, R₀₁ and R₀₂ may be either amonocyclic type or a polycyclic type. The monocyclic type is preferablya cycloalkyl group having a carbon number of 3 to 8, and examplesthereof include a cyclopropyl group, a cyclobutyl group, a cyclopentylgroup, a cyclohexyl group and a cyclooctyl group. The polycyclic type ispreferably a cycloalkyl group having a carbon number of 6 to 20, andexamples thereof include an adamantyl group, a norbomyl group, anisoboronyl group, a camphomyl group, a dicylopentyl group, an α-pinelgroup, a tricyclodecanyl group, a tetracyclododecyl group and anandrostanyl group. In the cycloalkyl group, the carbon atom may bepartially substituted by a heteroatom such as oxygen atom.

The aryl group of R₃₆ to R₃₉, R₀₁ and R₀₂ is preferably an aryl grouphaving a carbon atom of 6 to 10, and examples thereof include a phenylgroup, a naphthyl group and an anthryl group.

The aralkyl group of R₃₆ to R₃₉, R₀₁ and R₀₂ is preferably an aralkylgroup having a carbon number of 7 to 12, and examples thereof include abenzyl group, a phenethyl group and a naphthylmethyl group.

The alkenyl group of R₃₆ to R₃₉, R₀₁ and R₀₂ is preferably an alkenylgroup having a carbon number of 2 to 8, and examples thereof include avinyl group, an allyl group, a butenyl group and a cyclohexenyl group.

R₃₆ to R₃₉, R₀₁ and R₀₂ each may have a substituent. Examples of thesubstituent which R₃₆ to R₃₉, R₀₁ and R₀₂ each may have include an alkylgroup, a cycloalkyl group, an aryl group, an amino group, an amidogroup, a ureido group, a urethane group, a hydroxyl group, a carboxylgroup, a halogen atom, an alkoxy group, a thioether group, an acylgroup, an acyloxy group, an alkoxycarbonyl group, a cyano group and anitro group.

Formula (C) is preferably represented by the following formula (C1):

In formula (C1), X₁, X₂ and X₃ each independently represents a hydrogenatom, an alkyl group or a halogen atom.

R₁₂, R₁₃ and R₁₄ each independently represents an alkyl group, acycloalkyl group, an alkenyl group or an aryl group, or a monovalentgroup formed by bonding at least two of these groups, provided that atleast one of R₁₂, R₁₃ and R₁₄ represents an alkyl group, and two membersout of R₁₂, R₁₃ and R₁₄ may combine to form a ring.

X₁, X₂ and X₃ in formula (C1) have the same meanings as XI, X₂ and X₃ informula (C).

The alkyl group, cycloalkyl group, alkenyl group and aryl group of R₁₂,R₁₃ and R₁₄ are the same as the alkyl group, cycloalkyl group, alkenylgroup and aryl group of R₃₆ to R₃₈ in the above-described group which isdetached under the action of an acid.

The repeating unit represented by formula (C1) is preferably a repeatingunit where R₁₂, R₁₃ and R₁₄ each is independently an alkyl group or analkenyl group and at least one of R₁₂, R₁₃ and R₁₄ is an alkyl group.

In the resin (C1), R₁₂, R₁₃ and R₁₄ each independently represents analkyl group, an alkenyl group or a cycloalkyl group, or a monovalentgroup formed by bonding at least two of these groups, and the number ofcarbon atoms contained in R₁₂ to R₁₄ is from 6 to 20.

Specific examples of the repeating unit represented by formula (C) areset forth below, but the present invention is not limited thereto.

In specific examples above, Rx represents a hydrogen atom or a methylgroup.

Rxa, Rxb and Rxc each independently represents an alkyl group having acarbon number of 1 to 4.

Rxx represents a hydrogen atom or an alkyl group having a carbon numberof 1 to 4.

The resin as the component (C) may contain other repeating units inaddition to the repeating unit represented by formula (C).

Examples of the other repeating unit which the resin as the component(C) may have include a repeating unit represented by the followingformula (C2):

In formula (C2), X₄, X₅ and X₆ each independently represents a hydrogenatom, an alkyl group or a halogen atom.

L₁ represents a single bond or a divalent linking group.

Rp₂ represents a non-acid-decomposable group.

X₄, X₅ and X₆ in formula (C2) are the same as X₁, X₂ and X₃ in formula(C).

The divalent linking group of L₂ is the same as the divalent linkinggroup of L in formula (C). The divalent linking group of L₂ ispreferably an alkylene group, an ester group and an ether group.

Examples of the non-acid-decomposable group of Rp₂ include a linear orbranched alkyl group (preferably having a carbon number of 2 to 20), acycloalkyl group (preferably having a carbon number of 3 to 20), an arylgroup (preferably having a carbon number of 6 to 15), an alkenyl group(preferably having a carbon number of 2 to 10), which are incapable ofdecomposing under the action of an acid to produce an alkali-solublegroup. This non-acid-decomposable group is preferably a branched alkylgroup, a cycloalkyl group or an alkenyl group.

Examples of the other repeating unit which the resin as the component(C) may have further include a repeating unit represented by formula(VIII) in the resin as the component (A).

The resin as the component (C) preferably comprises a repeating unitrepresented by formula (C1) and a repeating unit represented by formula(C2) in a proportion of 80 to 100 mol %, more preferably from 90 to I 00mol % in total repeating units.

In formulae (C1) and (C2), X₁, X₂, X₃, X4, X₅ and X₆ each independentlyrepresents a hydrogen atom, an alkyl group or a halogen atom.

R₁₂, R₁₃ and R₁₄ each independently represents an alkyl group, acycloalkyl group, an alkenyl group or an aryl group, or a monovalentgroup formed by bonding at least two of these groups, provided that atleast one of R₁₂, R₁₃ and R₁₄ represents an alkyl group, and two membersout of R₁₂, R₁₃ and R₁₄ may combine to form a ring.

L₁ represents a single bond or a divalent linking group.

RP₂ represents a non-acid-decomposable group.

m and n each represents a molar ratio of the repeating unit, and m=10 to100, n=0 to 90 and m+n=100.

The resin as the component (C) preferably further contains a repeatingunit selected from the following formulae (C-I) to (C-IV) in aproportion of 80 to 100 mol % in total repeating units, provided thatthe repeating unit represented by formula (C-I) is used in combinationwith the repeating unit represented by formula (C-II):

In formulae (C-1) to (C-IV), R₁ represents a hydrogen atom or a methylgroup;

R₂ represents a hydrocarbon group having two or more —CH₃ partialstructures, provided that when a plurality of R₂'s are present, theplurality of R₂'s may be the same or different;

P₁ represents a single bond, an alkylene group or an ether group, or alinking group having two or more thereof;

P₂ represents a linking group selected from —O—, —NR— and —NHSO₂—,wherein R represents a hydrogen atom or an alkyl group;

x1, x2, y and z represent mol % in total repeating units, and x1represents a number of 0 to 50, x2 represents a number of 0 to 50, yrepresents a number of 0 to 100, z represents a number of 0 to 100,provided that x1, x2, y and z satisfy 80≦x1+x2+y+z≦100; and

n represents an integer of from 1 to 4.

The hydrocarbon group having at least two —CH₃ partial structures of R₂in formulae (C-I) to (C-IV) includes, for example, an alkyl group, analkyloxy group, an alkyl-substituted cycloalkyl group, analkyl-substituted alkenyl group, an alkyl-substituted aryl group and analkyl-substituted aralkyl group each having at least two —CH₃ partialstructures. An alkyl group and an alkyl-substituted cycloalkyl groupeach having at least two —CH₃ partial structures are preferred.

Examples of the hydrocarbon group having at least two —CH₃ partialstructures of R₂ in formulae (C-I) to (C-IV) include an alkyl grouphaving at least two —CH₃ partial structures, an alkyloxy group having atleast two —CH₃ partial structures, a cycloalkyl group substituted by atleast two alkyl groups having one —CH₃ partial structure or by at leastone alkyl group having at least two —CH₃ partial structures, an alkenylgroup substituted by at least two alkyl groups having one —CH₃ partialstructure or by at least one alkyl group having at least two —CH₃partial structures, an aryl group substituted by at least two alkylgroups having one —CH₃ partial structure or by at least one alkyl grouphaving at least two —CH₃ partial structures, and an aralkyl groupsubstituted by at least two alkyl groups having one —CH₃ partialstructure or by at least one alkyl group having at least two —CH₃partial structures. Among these, preferred are an alkyl group having atleast two —CH₃ partial structures, an alkyloxy group having at least two—CH₃ partial structures, and a cycloalkyl group substituted by at leasttwo alkyl groups having one —CH₃ partial structure or by at least onealkyl group having at least two —CH₃ partial structures. The alkyl grouphaving at least two —CH₃ partial structures may be substituted by acycloalkyl group.

The alkyl group having at least two —CH₃ partial structures of R₂ ispreferably a branched alkyl group having a carbon number of 3 to 20.Specific preferred examples of the alkyl group include an isopropylgroup, an isobutyl group, a tert-butyl group, a 3-pentyl group, a2-methyl-3-butyl group, a 3-hexyl group, a 2-methyl-3-pentyl group, a3-methyl-4-hexyl group, a 3,5-dimethyl-4-pentyl group, an isooctylgroup, a 2,4,4-trimethylpentyl group, a 2-ethylhexyl group, a2,6-dimethylheptyl group, a 1,5-dimethyl-3-heptyl group and a2,3,5,7-tetramethyl-4-heptyl group. Among these, more preferred are anisobutyl group, a tert-butyl group, a 2-methyl-3-butyl group, a2-methyl-3-pentyl group, a 3-methyl-4-hexyl group, a3,5-dimethyl-4-pentyl group, a 2,4,4-trimethylpentyl group, a2-ethylhexyl group, a 2,6-dimethylheptyl group, a 1,5-dimethyl-3-heptylgroup and a 2,3,5,7-tetramethyl-4-heptyl group.

The alkyl group having one —CH₃ partial structure of R₂ is preferably alinear alkyl group having a carbon number of 1 to 20. Specific preferredexamples of the alkyl group include a methyl group, an ethyl group, apropyl group, a butyl group, a pentyl group, a hexyl group, a heptylgroup, an octyl group and a nonyl group.

The alkyloxy group having at least two —CH₃ partial structures of R₂includes a group resulting from bonding of an ether group to an alkylgroup having at least two —CH₃ partial structures.

The cycloalkyl group of R₂ may be monocyclic or polycyclic andspecifically includes a group having a carbon number of 5 or more andhaving a monocyclo, bicyclo, tricyclo or tetracyclo structure or thelike. The carbon number thereof is preferably from 6 to 30, morepreferably from 7 to 25. Preferred examples of the cycloalkyl groupinclude an adamantyl group, a noradamantyl group, a decalin residue, atricyclodecanyl group, a tetracyclododecanyl group, a norbomyl group, acedrol group, a cyclopentyl group, a cyclohexyl group, a cycloheptylgroup, a cyclooctyl group, a cyclodecanyl group and a cyclododecanylgroup. Among these, more preferred are an adamantyl group, a norbomylgroup, a cyclohexyl group, a cyclopentyl group, a tetracyclododecanylgroup and a tricyclodecanyl group, and still more preferred are anorbomyl group, a cyclopentyl group and a cyclohexyl group.

The alkenyl group of R₂ is preferably a linear or branched alkenyl grouphaving a carbon number of 1 to 20, more preferably a branched alkenylgroup.

The aryl group of R₂ is preferably an aryl group having a carbon numberof 6 to 20, and examples thereof include a phenyl group and a naphthylgroup, with a phenyl group being preferred.

The aralkyl group of R₂ is preferably an aralkyl group having a carbonnumber of 7 to 12, and examples thereof include a benzyl group, aphenethyl group and a naphthylmethyl group.

Specific examples of the hydrocarbon group having at least two —CH₃partial structures of R₂ in formulae (C-I) and (C-III) include anisopropyl group, an isobutyl group, a tert-butyl group, a 3-pentylgroup, a 2-methyl-3-butyl group, a 3-hexyl group, a 2,3-dimethyl-2-butylgroup, a 2-methyl-3-pentyl group, a 3-methyl-4-hexyl group, a3,5-dimethyl-4-pentyl group, an isooctyl group, a 2,4,4-trimethylpentylgroup, a 2-ethylhexyl group, a 2,6-dimethylheptyl group, a1,5-dimethyl-3-heptyl group, a 2,3,5,7-tetramethyl-4-heptyl group, a3,5-dimethylcyclohexyl group, a 4-isopropylcyclohexyl group, a4-tert-butylcyclohexyl group and an isobornyl group. Among these,preferred are an isobutyl group, a tert-butyl group, a 2-methyl-3-butylgroup, a 2,3-dimethyl-2-butyl group, a 2-methyl-3-pentyl group, a3-methyl-4-hexyl group, a 3,5-dimethyl-4-pentyl group, a2,4,4-trimethylpentyl group, a 2-ethylhexyl group, a 2,6-dimethylheptylgroup, a 1,5-dimethyl-3-heptyl group, a 2,3,5,7-tetramethyl-4-heptylgroup, a 3,5-dimethylcyclohexyl group, a 4-isopropylcyclohexyl group, a4-tert-butylcyclohexyl group and an isobornyl group.

Specific examples of the hydrocarbon group having at least two —CH₃partial structures of R₂ in formula (C-IV) include an isobutyl group, atert-butyl group, a 3-pentyl group, a 2,3-dimethylbutyl group, a2-methyl-3-butyl group, a 3-hexyl group, a 2-methyl-3-pentyl group, a3-methyl-4-hexyl group, a 3,5-dimethyl-4-pentyl group, an isooctylgroup, a 2,4,4-trimethylpentyl group, a 2-ethylhexyl group, a2,6-dimethylheptyl group, a 1,5-dimethyl-3-heptyl group, a2,3,5,7-tetramethyl-4-heptyl group, a 3,5-dimethylcyclohexyl group, a4-isopropylcyclohexyl group and a 4-tert-butylcyclohexyl group. Amongthese, preferred are an isobutyl group, a tert-butyl group, a2-methyl-3-butyl group, a 2-methyl-3-pentyl group, a 3-methyl-4-hexylgroup, a 3,5-dimethyl-4-pentyl group, a 2,4,4-trimethylpentyl group, a2-ethylhexyl group, a 2,6-dimethylheptyl group, a 1,5-dimethyl-3-heptylgroup, a 2,3,5,7-tetramethyl-4-heptyl group, a 2,6-dimethylheptyl group,a 3,5-dimethylcyclohexyl group, a 4-isopropylcyclohexyl group and a4-tert-butylcyclohexyl group.

In the resin having a repeating unit selected from formulae (C-I) to(C-IV), 80≦x1+x2+y+z≦100, preferably 85≦x1+x2+y+z≦100, more preferably90≦x1+x2+y+z≦100.

In the resin having a repeating unit selected from formulae (C-I) to(C-IV), at least one repeating unit selected from formulae (C-I) to(C-IV) preferably has an acid-decomposable group.

Examples of the acid-decomposable group in formulae (C-I) to (C-IV) arethe same as those of the acid-decomposable group of Rp, in formula (C).

Specific preferred examples of the repeating units represented byformulae (C-I) and (C-II) are set forth below, but the present inventionis not limited thereto.

Specific preferred examples of the repeating unit represented by formula(C-III) are set forth below, but the present invention is not limitedthereto.

In formula (C-IV), when P₂ is oxygen atom, the carbon atom directlybonded to the oxygen atom is preferably secondary or tertiary and in thecase of a tertiary carbon atom, the structure becomes the same as thatof the repeating unit represented by formula (C1).

Specific preferred examples of the repeating unit represented by formula(C-IV), other than the repeating unit represented by formula (C1), areset forth below, but the present invention is not limited thereto. Inspecific examples, Rxy represents a hydrogen atom or a methyl group.

The resin as the component (C) preferably has no silicon atom and nofluorine tom.

The resin as the component (C) preferably has no element other thancarbon atom, hydrogen atom, oxygen atom, nitrogen atom and sulfur atom.

The resin as the component (C) preferably contains a repeating unithaving an acid-decomposable group at a proportion of 5 to 100 mol %,more preferably from 10 to 100 mol %.

The resin as the component (C) preferably has a weight average molecularweight of 1,500 to 100,000, more preferably from 2,000 to 70,000, stillmore preferably from 3,000 to 50,000, particularly preferably from 3,000to 15,000. The resin as the component (C) preferably has a dispersity(Mw/Mn) of 1.0 to 3.0, more preferably from 1.2 to 2.5, still morepreferably from 1.2 to 2.0.

The resin as the component (C) may be synthesized in the same manner asthe resin of the component (A). A chain transfer agent can be usedaccording to necessity.

The content of the resin as the component (C) is from 0.1 to 20 mass %,preferably from 0.1 to 10 mass %, more preferably from 0.1 to 5 mass %,still more preferably from 0.1 to 3 mass %, yet still more preferablyfrom 0.5 to 2 mass %, based on the solid content of the positive resistcomposition (all solid contents constituting the resist film).

[4] (D) Organic Solvent

Examples of the solvent which can be used for dissolving respectivecomponents described above to prepare a positive resist compositioninclude an alkylene glycol monoalkyl ether carboxylate, an alkyleneglycol monoalkyl ether, an alkyl lactate, an alkyl alkoxypropionate, acyclic lactone having a carbon number of 4 to 10, a monoketone compoundhaving a carbon number of 4 to 10 which may contain a ring, an alkylenecarbonate, an alkyl alkoxyacetate and an alkyl pyruvate.

Preferred examples of the alkylene glycol monoalkyl ether carboxylateinclude propylene glycol monomethyl ether acetate, propylene glycolmonoethyl ether acetate, propylene glycol monopropyl ether acetate,propylene glycol monobutyl ether acetate, propylene glycol monomethylether propionate, propylene glycol monoethyl ether propionate, ethyleneglycol monomethyl ether acetate and ethylene glycol monoethyl etheracetate.

Preferred examples of the alkylene glycol monoalkyl ether includepropylene glycol monomethyl ether, propylene glycol monoethyl ether,propylene glycol monopropyl ether, propylene glycol monobutyl ether,ethylene glycol monomethyl ether and ethylene glycol monoethyl ether.

Preferred examples of the alkyl lactate include methyl lactate, ethyllactate, propyl lactate and butyl lactate.

Preferred examples of the alkyl alkoxypropionate include ethyl3-ethoxypropionate, methyl 3-methoxypropionate, methyl3-ethoxypropionate and ethyl 3-methoxypropionate.

Preferred examples of the cyclic lactone having a carbon number of 4 to10 include β-propiolactone, β-butyrolactone, γ-butyrolactone,α-methyl-γ-butyrolactone, β-methyl-γ-butyrolactone, γ-valerolactone,γ-caprolactone, γ-octanoic lactone and α-hydroxy-γ-butyrolactone.

Preferred examples of the monoketone compound having a carbon number of4 to 10 which may contain a ring include 2-butanone, 3-methylbutanone,pinacolone, 2-pentanone, 3-pentanone, 3-methyl-2-pentanone,4-methyl-2-pentanone, 2-methyl-3-pentanone, 4,4-dimethyl-2-pentanone,2,4-dimethyl-3-pentanone, 2,2,4,4-tetramethyl-3-pentanone, 2-hexanone,3-hexanone, 5-methyl-3-hexanone, 2-heptanone, 3-heptanone, 4-heptanone,2-methyl-3-heptanone, 5-methyl-3-heptanone, 2,6-dimethyl-4-heptanone,2-octanone, 3-octanone, 2-nonanone, 3-nonanone, 5-nonanone, 2-decanone,3-decanone, 4-decanone, 5-hexen-2-one, 3-penten-2-one, cyclopentanone,2-methylcyclopentanone, 3-methylcyclopentanone,2,2-dimethylcyclopentanone, 2,4,4-trimethylcyclopentanone,cyclohexanone, 3-methylcyclohexanone, 4-methylcyclohexanone,4-ethylcyclohexanone, 2,2-dimethylcyclohexanone,2,6-dimethylcyclohexanone, 2,2,6-trimethylcyclohexanone, cycloheptanone,2-methylcycloheptanone and 3-methylcycloheptanone.

Preferred examples of the alkylene carbonate include propylenecarbonate, vinylene carbonate, ethylene carbonate and butylenecarbonate.

Preferred examples of the alkyl alkoxyacetate include 2-methoxyethylacetate, 2-ethoxyethyl acetate, 2-(2-ethoxyethoxy)ethyl acetate,3-methoxy-3-methylbutyl acetate and 1-methoxy-2-propyl acetate.

Preferred examples of the alkyl pyruvate include methyl pyruvate, ethylpyruvate and propyl pyruvate.

The solvent which can be preferably used includes a solvent having aboiling point of 130° C. or more at ordinary temperature and atmosphericpressure, and specific examples thereof include cyclopentanone,γ-butyrolactone, cyclohexanone, ethyl lactate, ethylene glycol monoethylether acetate, propylene glycol monomethyl ether acetate, ethyl3-ethoxypropionate, ethyl pyruvate, 2-ethoxyethyl acetate,2-(2-ethoxyethoxy)ethyl acetate and propylene carbonate.

In the present invention, one of these solvents may be used alone, ortwo or more species thereof may be used in combination.

In the present invention, a mixed solvent prepared by mixing a solventcontaining a hydroxyl group in the structure and a solvent notcontaining a hydroxyl group may be used as the organic solvent.

Examples of the solvent containing a hydroxyl group include ethyleneglycol, ethylene glycol monomethyl ether, ethylene glycol monoethylether, propylene glycol, propylene glycol monomethyl ether, propyleneglycol monoethyl ether and ethyl lactate. Among these, propylene glycolmonomethyl ether and ethyl lactate are preferred.

Examples of the solvent not containing a hydroxyl group includepropylene glycol monomethyl ether acetate, ethyl ethoxypropionate,2-heptanone, γ-butyrolactone, cyclohexanone, butyl acetate,N-methylpyrrolidone, N,N-dimethylacetamide and dimethylsulfoxide. Amongthese, propylene glycol monomethyl ether acetate, ethylethoxy-propionate, 2-heptanone, γ-butyrolactone, cyclohexanone and butylacetate are preferred, and propylene glycol monomethyl ether acetate,ethyl ethoxypropionate and 2-heptanone are most preferred.

The mixing ratio (by mass) between the hydroxyl group-containing solventand the hydroxyl group-free solvent is from 1/99 to 99/1, preferablyfrom 10/90 to 90/10, more preferably from 20/80 to 60/40. A mixedsolvent containing a hydroxy group-free solvent in a proportion of 50mass % or more is preferred in view of coating uniformity.

[5] (E) Basic Compound

The positive resist composition of the present invention preferablycomprises (E) a basic compound for reducing the change of performance inaging from exposure until heating.

Preferred examples of the basic compound include compounds having astructure represented by any one of the following formulae (A) to (E):

In formulae (A) to (E), R²⁰⁰, R²⁰¹ and R²⁰², which may be the same ordifferent, each represents a hydrogen atom, an alkyl group having acarbon number of 1 to 20, a cycloalkyl group having a carbon number of 3to 20, or an aryl group having a carbon number of 6 to 20, and R²⁰¹ andR²⁰² may combine with each other to form a ring.

The alkyl group may be unsubstituted or may be an alkyl group having asubstituent, and the alkyl group having a substituent is preferably anaminoalkyl group having a carbon number of 1 to 20, a hydroxyalkyl grouphaving a carbon number of 1 to 20, or a cyanoalkyl group having a carbonnumber of 1 to 20.

R²⁰³, R²⁰⁴, R²⁰⁵ and R²⁰⁶, which may be the same or different, eachrepresents an alkyl group having a carbon number of 1 to 20.

The alkyl group in these formulae (A) to (E) is more preferablyunsubstituted.

Examples of the basic compound include substituted or unsubstitutedprimary, secondary or tertiary aliphatic amines, aromatic amines,heterocyclic amines, amide derivatives, imide derivatives, andnitrogen-containing compounds having a cyano group. Among these,aliphatic amines, aromatic amines and heterocyclic amines are preferred.Preferred substituents which these compounds each may have include anamino group, an alkyl group, an alkoxyl group, an acyl group, an acyloxygroup, an aryl group, an aryloxy group, a nitro group, a cyano group, anester group and a lactone group.

Preferred examples of the compound include guanidine, aminopyrrolidine,pyrazole, pyrazoline, piperazine, aminomorpholine, aminoalkylmorpholineand piperidine, and these compounds each may have a substituent. Morepreferred examples of the compound include a compound having animidazole structure, a diazabicyclo structure, an onium hydroxidestructure, an onium carboxylate structure, a trialkylamine structure, ananiline structure or a pyridine structure; an alkylamine derivativehaving a hydroxyl group and/or an ether bond; and an aniline derivativehaving a hydroxyl group and/or an ether bond.

Examples of the compound having an imidazole structure includeimidazole, 2,4,5-triphenylimidazole and benzimidazole. Examples of thecompound having a diazabicyclo structure include1,4-diazabicyclo[2,2,2]octane, 1,5-diazabicyclo[4,3,O]non-5-ene and1,8-diazabicyclo[5,4,0]undec-7-ene. Examples of the compound having anonium hydroxide structure include triarylsulfonium hydroxide,phenacylsulfonium hydroxide and sulfonium hydroxide having a 2-oxoalkylgroup, specifically, triphenylsulfonium hydroxide,tris(tert-butylphenyl)sulfonium hydroxide, bis(tert-butylphenyl)iodoniumhydroxide, phenacylthiophenium hydroxide and 2-oxopropylthiopheniumhydroxide. Examples of the compound having an onium carboxylatestructure include a compound where the anion moiety of the compoundhaving an onium hydroxide structure is converted into a carboxylate,such as acetate, adamantane-1-carboxylate and perfluoroalkylcarboxylate. Examples of the compound having a trialkylamine structureinclude tri(n-butyl)amine and tri(n-octyl)amine. Examples of the anilinecompound include 2,6-diisopropylaniline and N,N-dimethylaniline.Examples of the alkylamine derivative having a hydroxyl group and/or anether bond include ethanolamine, diethanolamine, triethanolamine andtris(methoxyethoxyethyl)amine. Examples of the aniline derivative havinga hydroxyl group and/or an ether bond includeN,N-bis(hydroxyethyl)aniline.

One of these basic compounds is used alone, or two or more speciesthereof are used in combination.

The amount of the basic compound used is usually from 0.001 to 10 mass%, preferably from 0.01 to 5 mass %, based on the solid content of thepositive resist composition.

The ratio between the acid generator and the basic compound used in thecomposition is preferably acid generator/basic compound (by mol)=from2.5 to 300. That is, the molar ratio is preferably 2.5 or more in viewof sensitivity and resolution and preferably 300 or less from thestandpoint of suppressing the reduction in resolution due to thickeningof the resist pattern in aging after exposure until heat treatment. Theratio of acid generator/basic compound (by mol) is more preferably from5.0 to 200, still more preferably from 7.0 to 150.

[6] (F) Surfactant

The positive resist composition of the present invention preferablyfurther comprises (F) a surfactant, more preferably any onefluorine-containing and/or silicon-containing surfactant (afluorine-containing surfactant, a silicon-containing surfactant, or asurfactant containing both a fluorine atom and a silicon atom), or twoor more species thereof.

When the positive resist composition of the present invention containsthe (F) surfactant, a resist pattern with good sensitivity, resolutionand adhesion as well as less development defects can be obtained when anexposure light source of 250 nm or less, particularly 220 nm or less, isused.

Examples of the fluorine-containing and/or silicon-containing surfactantinclude surfactants described in JP-A-62-36663, JP-A-61-226746,JP-A-61-226745, JP-A-62-170950, JP-A-63-34540, JP-A-7-230165,JP-A-8-62834, JP-A-9-54432, JP-A-9-5988, JP-A-2002-277862 and U.S. Pat.Nos. 5,405,720, 5,360,692, 5,529,881, 5,296,330, 5,436,098, 5,576,143,5,294,511 and 5,824,451. The following commercially availablesurfactants each may also be used as it is.

Examples of the commercially available surfactant which can be usedinclude a fluorine-containing surfactant and a silicon-containingsurfactant, such as EFtop EF301 and EF303 (produced by Shin-Akita KaseiK. K.); Florad FC430, 431 and 4430 (produced by Sumitomo 3M Inc.);Megafac F171, F173, F176, F189, F113, F110, F177, F120 and R08 (producedby Dainippon Ink & Chemicals, Inc.); Surflon S-382, SC101, 102, 103,104, 105 and 106 (produced by Asahi Glass Co., Ltd.); Troysol S-366(produced by Troy Chemical); GF-300 and GF-150 (produced by ToagoseiChemical Industry Co., Ltd.); Surflon S-393 (produced by Seimi ChemicalCo., Ltd.); Eftop EF121, EF122A, EF122B, RF122C, EF125M, EF135M, EF351,352, EF801, EF802 and EF601 (produced by JEMCO Inc.); PF636, PF656,PF6320 and PF6520 (produced by OMNOVA); and FTX-204D, 208G, 218G, 230G,204D, 208D, 212D, 218 and 222D (produced by NEOS Co., Ltd.). Inaddition, polysiloxane polymer KP-341 (produced by Shin-Etsu ChemicalCo., Ltd.) may also be used as the silicon-containing surfactant.

Other than those known surfactants, a surfactant using a polymer havinga fluoro-aliphatic group derived from a fluoro-aliphatic compound whichis produced by a telomerization process (also called a telomer process)or an oligomerization process (also called an oligomer process), may beused. The fluoro-aliphatic compound can be synthesized by the methoddescribed in JP-A-2002-90991.

The polymer having a fluoro-aliphatic group is preferably a copolymer ofa fluoro-aliphatic group-containing monomer with a (poly(oxyalkylene))acrylate and/or a (poly(oxyalkylene))methacrylate, and the polymer mayhave an irregular distribution or may be a block copolymer. Examples ofthe poly(oxyalkylene) group include a poly(oxyethylene) group, apoly(oxypropylene) group and a poly(oxybutylene) group. This group mayalso be a unit having alkylenes differing in the chain length within thesame chain, such as block-linked poly(oxyethylene, oxypropylene andoxyethylene) and block-linked poly(oxyethylene and oxypropylene).Furthermore, the copolymer of a fluoro-aliphatic group-containingmonomer and a (poly(oxyalkylene))acrylate (or methacrylate) may be notonly a binary copolymer but also a ternary or greater copolymer obtainedby simultaneously copolymerizing two or more different fluoro-aliphaticgroup-containing monomers or two or more different(poly(oxyalkylene))acrylates (or methacrylates).

Examples thereof include, as the commercially available surfactant,Megafac F178, F-470, F-473, F-475, F-476 and F-472 (produced byDainippon Ink & Chemicals, Inc.) and further include a copolymer of aC₆F₁₃ group-containing acrylate (or methacrylate) with a(poly(oxyalkylene))acrylate (or methacrylate), and a copolymer of a C₃F₇group-containing acrylate (or methacrylate) with a(poly(oxyethylene))acrylate (or methacrylate) and a(poly(oxypropylene))acrylate (or methacrylate).

In the present invention, a surfactant other than thefluorine-containing and/or silicon-containing surfactant may also beused. Specific examples thereof include a nonionic surfactant such aspolyoxyethylene alkyl ethers (e.g., polyoxyethylene lauryl ether,polyoxyethylene stearyl ether, polyoxyethylene cetyl ether,polyoxyethylene oleyl ether), polyoxyethylene alkylallyl ethers (e.g.,polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether),polyoxyethylene-polyoxypropylene block copolymers, sorbitan fatty acidesters (e.g., sorbitan monolaurate, sorbitan monopalmitate, sorbitanmonostearate, sorbitan monooleate, sorbitan trioleate, sorbitantristearate), and polyoxyethylene sorbitan fatty acid esters (e.g.,polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitanmonopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylenesorbitan trioleate, polyoxyethylene sorbitan tristearate).

One of these surfactants may be used alone, or several species thereofmay be used in combination.

The amount of the (F) surfactant used is preferably from 0.01 to 10 mass%, more preferably from 0.1 to 5 mass %, based on the entire amount ofthe positive resist composition (excluding the solvent).

[7] (G) Onium Carboxylate

The positive resist composition of the present invention may comprise anonium carboxylate. Examples of the onium carboxylate include sulfoniumcarboxylate, iodonium carboxylate and ammonium carboxylate. Inparticular, the onium carboxylate is preferably an iodonium salt or asulfonium salt. Furthermore, the carboxylate residue of the oniumcarboxylate for use in the present invention preferably contains noaromatic group and no carbon-carbon double bond. The anion moiety ispreferably a linear, branched, monocyclic or polycyclic alkylcarboxylateanion having a carbon number of 1 to 30, more preferably an anion of thecarboxylic acid with the alkyl group being partially or entirelyfluorine-substituted. The alkyl chain may contain an oxygen atom. Byvirtue of such a construction, the transparency to light at 220 nm orless is ensured, the sensitivity and resolution are enhanced, and thedefocus latitude depended on line pitch and the exposure margin areimproved.

Examples of the anion of a fluorine-substituted carboxylic acid includeanions of fluoroacetic acid, difluoroacetic acid, trifluoroacetic acid,pentafluoropropionic acid, heptafluorobutyric acid, nonafluoropentanoicacid, perfluorododecanoic acid, perfluoro-tridecanoic acid,perfluorocyclohexanecarboxylic acid and 2,2-bistrifluoromethylpropionicacid.

These onium carboxylates can be synthesized by reacting silver oxidewith a sulfonium, iodonium or ammonium hydroxide and a carboxylic acidin an appropriate solvent.

The content of the onium carboxylate in the composition is suitably from0.1 to 20 mass %, preferably from 0.5 to 10 mass %, more preferably from1 to 7 mass %, based on the entire solid content of the composition.

Other Additives:

The positive resist composition of the present invention may furthercontain, for example, a dye, a plasticizer, a photosensitizer, a lightabsorbent, an alkali-soluble resin, a dissolution inhibitor, and acompound for accelerating dissolution in a developer (for example, aphenol compound having a molecular weight of 1,000 or less, or acarboxyl group-containing alicyclic or aliphatic compound), if desired.

The phenol compound having a molecular weight of 1,000 or less can beeasily synthesized by one skilled in the art with reference to themethods described, for example, in JP-A-4-122938, JP-A-2-28531, U.S.Pat. No. 4,916,210 and European Patent 219294.

Specific examples of the carboxyl group-containing alicyclic oraliphatic compound include, but are not limited to, a carboxylic acidderivative having a steroid structure, such as cholic acid, deoxycholicacid and lithocholic acid, an adamantanecarboxylic acid derivative, anadamantanedicarboxylic acid, a cyclohexanecarboxylic acid and acyclohexanedicarboxylic acid.

[Physical Properties of Resist Composition]

The positive resist composition of the present invention is preferablyused in a film thickness of 30 to 250 nm, more preferably from 30 to 200nm, from the standpoint of enhancing the resolving power. Such a filmthickness can be obtained by setting the solid content concentration inthe positive resist composition to an appropriate range and therebygiving an appropriate viscosity to enhance the coatability andfilm-forming property.

The entire solid content concentration in the positive resistcomposition is generally from 1 to 10 mass %, preferably from 1 to 8mass %, more preferably from 1.0 to 7.0 mass %, still more preferablyfrom 1.0 to 6.0 mass %.

[Pattern Forming Method]

The positive resist composition of the present invention is used bydissolving the components described above in a predetermined organicsolvent, preferably in the above-described mixed solvent, filtering thesolution, and coating it on a predetermined support as follows. Thefilter used for filtering is preferably a filter made ofpolytetrafluoroethylene, polyethylene or nylon and having a pore size of0.1 micron or less, more preferably 0.05 microns or less, still morepreferably 0.03 microns or less.

For example, the positive resist composition is coated on a substrate(e.g., silicon/silicon dioxide-coated substrate) as used in theproduction of a precision integrated circuit device, by an appropriatecoating method such as spinner or coater, and then dried to form aresist film.

From the standpoint of enhancing the resolving power, the positiveresist composition of the present invention is preferably used in a filmthickness of 30 to 500 nm, more preferably from 30 to 250 nm, still morepreferably from 30 to 200 nm.

This resist film is irradiated with actinic rays or radiation through apredetermined mask, preferably baked (heated), then developed andrinsed, whereby a good resist pattern can be obtained.

Examples of the actinic rays or radiation include infrared light,visible light, ultraviolet light, far ultraviolet light, X-ray andelectron beam, but the radiation is preferably far ultraviolet light ata wavelength of 250 nm or less, more preferably 220 nm or less, stillmore preferably from 1 to 200 nm. Specific examples thereof include KrFexcimer laser light (248 nm), ArF excimer laser light (193 nm), F₂excimer laser light (157 nm), X-ray and electron beam. ArF excimer laserlight, F₂ excimer laser light, EUV (13 nm) and electron beam arepreferred.

In the development step, an alkali developer is used as follows. Thealkali developer which can be used for the resist composition is analkaline aqueous solution of inorganic alkalis such as sodium hydroxide,potassium hydroxide, sodium carbonate, sodium silicate, sodiummetasilicate and aqueous ammonia, primary amines such as ethylamine andn-propylamine, secondary amines such as diethylamine anddi-n-butylamine, tertiary amines such as triethylamine andmethyldiethylamine, alcohol amines such as dimetylethanolamine andtriethanolamine, quaternary ammonium salts such as tetramethylammoniumhydroxide and tetraethylammonium hydroxide, and cyclic amines such aspyrrole and piperidine.

Furthermore, this alkali developer may be used after adding theretoalcohols and a surfactant each in an appropriate amount.

The alkali concentration of the alkali developer is usually from 0.1 to20 mass %.

The pH of the alkali developer is usually from 10.0 to 15.0.

Also, the above-described alkaline aqueous solution may be used afteradding thereto alcohols and a surfactant each in an appropriate amount.

As for the rinsing solution, pure water is used, and the pure water maybe used after adding thereto a surfactant in an appropriate amount.

The development or ringing may be performed by forming a puddle or by apuddleless process. In the case of immersion exposure, a rinsing stepmay be provided before and after the exposure.

After the development or rinsing, the developer or rinsing solutionadhering on the pattern may removed by a supercritical fluid.

The exposure may be performed by filling a liquid (immersion medium)having a refractive index higher than that of air between the resistfilm and a lens at the irradiation with actinic rays or radiation(immersion exposure). By this exposure, the resolution can be enhanced.The immersion medium used may be any liquid as long as it has arefractive index higher than that of air, but pure water is preferred.Also, in order to prevent the immersion medium and the photosensitivefilm from coming into direct contact at the immersion exposure, anovercoat layer may be further provided on the photosensitive film. Inthis case, the composition can be restrained from dissolving out intothe immersion medium from the photosensitive film and the developmentdefects can be reduced.

The immersion liquid used in the immersion exposure is described below.

The immersion liquid is preferably a liquid transparent to light at theexposure wavelength and having a small temperature coefficient ofrefractive index as much as possible so as to minimize the distortion ofan optical image projected on the resist. Particularly, when theexposure light source is an ArF excimer laser (wavelength: 193 nm),water is preferably used in view of easy availability and easyhandleability, in addition to the above-described aspects.

Furthermore, a medium having a refractive index of 1.5 or more may alsobe used because the refractive index can be more enhanced. This mediummay be either an aqueous solution or an organic solvent.

In the case of using water as the immersion liquid, for the purpose ofdecreasing the surface tension of water and increasing the surfaceactivity, an additive (liquid) which does not dissolve the resist layeron a wafer and at the same time, gives only a negligible effect on theoptical coat at the undersurface of the lens element, may be added in asmall ratio. The additive is preferably an aliphatic alcohol having arefractive index nearly equal to that of water, and specific examplesthereof include methyl alcohol, ethyl alcohol and isopropyl alcohol. Byadding an alcohol having a refractive index nearly equal to that ofwater, even when the alcohol component in water is evaporated and itscontent concentration is changed, the change in the refractive index ofthe entire liquid can be advantageously made very small. On the otherhand, if a substance opaque to light at 193 nm or an impurity greatlydiffering in the refractive index from water is mingled, this incursdistortion of the optical image projected on the resist. Therefore, thewater used is preferably distilled water. Pure water after furtherfiltration through an ion exchange filter or the like may also be used.

The electrical resistance of water is preferably 18.3 MQcm or more, andTOC (organic material concentration) is preferably 20 ppb or less. Also,the water is preferably subjected to a deaeration treatment.

The lithography performance can be enhanced by increasing the refractiveindex of the immersion liquid. From such an aspect, an additive forincreasing the refractive index may be added to water, or heavy water(D₂O) may be used in place of water.

In order to prevent the resist film -from directly contacting with theimmersion liquid, an immersion liquid sparingly soluble film(hereinafter, sometimes referred to as a “topcoat”) may be providedbetween the immersion liquid and the resist film formed of the positiveresist composition of the present invention. The functions required ofthe topcoat are suitability for coating on the resist upper layer part,transparency to radiation particularly at 193 nm, and low solubility inthe immersion liquid. It is preferred that the topcoat does not intermixwith the resist and can be uniformly coated on the resist upper layer.

In view of transparency to light at 193 nm, the topcoat preferablycomprises an aromatic-free polymer, and specific examples thereofinclude a hydrocarbon polymer, an acrylic acid ester polymer, apolymethacrylic acid, a polyacrylic acid, a polyvinyl ether, asilicon-containing polymer and a fluorine-containing polymer. Ifimpurities dissolve out into the immersion liquid from the topcoat, theoptical lens is contaminated. In this viewpoint, the topcoat preferablyless contains residual monomer components of the polymer.

On peeling off the topcoat, a developer may be used or a releasing agentmay be separately used. The releasing agent is preferably a solventwhich less permeates into the resist. From the standpoint that thepeeling step can be performed simultaneously with the resist developmentstep, the topcoat is preferably peelable with an alkali developer and inthe light of peeling with an alkali developer, the topcoat is preferablyacidic, but in view of non-intermixing with the resist, the topcoat maybe neutral or alkaline.

With no difference in the refractive index between the topcoat and theimmersion liquid, the resolving power is enhanced. At the exposure withan ArF excimer laser (wavelength: 193 nm), when water is used as theimmersion liquid, the topcoat for ArF immersion exposure preferably hasa refractive index close to the refractive index of the immersionliquid. From the standpoint of approximating the refractive index tothat of the immersion liquid, the topcoat preferably contains a fluorineatom. Also, in view of transparency and refractive index, the topcoat ispreferably a thin film.

The topcoat is preferably free of intermixing with the resist andfurther with the immersion liquid. From this standpoint, when theimmersion liquid is water, the topcoat solvent is preferably a mediumwhich is sparingly soluble in the resist solvent and insoluble in water.Furthermore, when the immersion liquid is an organic solvent, thetopcoat may be either water-soluble or water-insoluble.

When the positive resist composition of the present invention is used,the resin (C) contained in the resist is unevenly distributed to thesurface, so that the contact angle (particularly receding contact angle)on the film surface can be enhanced. When formed as a resist film, thereceding contact angle of water for the resist film is preferably 60° ormore, more preferably 65° or more, still more preferably 70° or more.Also, when only the resin (C) is dissolved in a solvent and theresulting solution is coated, the receding contact angle of the filmformed is preferably from 70 to 110°. The receding contact angle of theresist film on use is adjusted to 60 to 80° by controlling the amount ofthe resin (C) added.

The receding contact angle here is a receding contact angle at ordinarytemperature and atmospheric pressure. The receding contact angle is acontact angle on the receding end of a liquid droplet when the liquiddroplet starts sliding down after the resist film is inclined.

EXAMPLES

The present invention is described in greater detail below by referringto Examples, but the present invention should not be construed as beinglimited thereto.

Synthesis Example 1 (Synthesis of Resin (C-1))

Ethyl methacrylate and tert-butyl methacrylate were charged at a ratioof 50/50 (by mol) and dissolved in cyclohexanone to prepare 450 g of asolution having a solid content concentration of 22 mass %. To thissolution, 5 mol % of polymerization initiator V-601 produced by WakoPure Chemical Industries, Ltd. was added. The resulting solution wasadded dropwise to 50 mL of cyclohexanone heated at 80° C., over 2 hoursin a nitrogen atmosphere. After the completion of dropwise addition, thesolution was stirred for 2 hours to obtain a reaction solution. Thereaction solution was cooled to room temperature and crystallized from a10-fold amount of methanol, and the precipitated white powder wascollected by filtration to recover the objective Resin (C-1).

The polymer compositional ratio (by mol) determined from ¹HNMR was50/50. Also, the weight average molecular weight determined by the GPCmeasurement and calculated in terms of standard polystyrene was 10,000,and the dispersity was 2.2.

Resins (C-2) to (C-20) as the component (C) were synthesized in the samemanner as in Synthesis Example 1.

The structures of Resins (C-1) to (C-20) are shown below.

The composition (molar ratio, corresponding to respective repeatingunits from the left), Mw (weight average molecular weight) and Mw/Mn(dispersity) in each of Resins (C-1) to (C-20) are shown in Table 1 andTable 2 below. TABLE 1 Resin Composition Mw Mw/Mn C-1 50/50 10000 2.2C-2 100 8500 1.8 C-3 40/60 12000 2.2 C-4 30/30/40 6700 2.0 C-5 50/509800 2.3 C-6 100 6800 1.8 C-7 40/60 4800 2.0 C-8 50/50 8500 2.2 C-920/20/60 9800 2.3 C-10 60/40 10000 2.2

TABLE 2 Resin Composition Mw Mw/Mn C-11 30/30/40 7000 2.0 C-12 100 80001.8 C-13 50/50 8000 2.0 C-14 50/50 8000 2.0 C-15 50/50 7500 2.3 C-1680/20 10000 2.1 C-17 70/30 10000 2.1 C-18 20/80 12000 2.2 C-19 30/50/2013000 2.0 C-20 40/50/10 13000 2.0

The structures of Resins (1) to (25) as the component (A) used inExamples are shown below.

The compostion (molar ratio, corresponding to respective repeating unitsfrom the left), Mw (wieght average molecular weight) and Mw/Mn(dispersity) in each of Resins (1) to (25) are shown in Table 3 andTable 4 below. TABLE 3 Resin Composition Mw Mw/Mn 1 24/30/46 9800 1.9 230/25/45 8500 2.0 3 34/33/33 11000 2.3 4 45/15/40 10500 2.1 5 30/25/458400 2.3 6 39/20/41 10500 2.1 7 49/10/41 9500 2.5 8 35/32/33 14000 2.6 940/20/35/5 12500 2.4 10 40/15/40/5 10000 1.8 11 40/15/40/5 9800 2.3 1235/20/40/5 6100 2.3 13 30/30/30/10 8600 2.5 14 40/20/35/5 12000 2.1 1550/50 5200 2.1

TABLE 4 Resin Composition Mw Mw/Mn 16 30/20/40/10 8000 2.0 17 40/10/506000 1.8 18 30/20/40/10 8500 1.5 19 35/30/35 9800 1.8 20 30/40/30 95001.9 21 25/25/50 6700 2.0 22 50/25/25 12000 2.0 23 50/30/20 10000 2.0 2440/20/20/10 6400 2.1 25 40/10/50 7700 2.0

Example 1 and 15 Comparative Examples 1 to 2

<Preparation of Resist>

The components shown in Table 5 below were dissolved in a solvent toprepare a solution having a solid content concentration of 6 mass %, andthe obtained solution was filtered through a 0.1-μm polyethylene filterto prepare a positive resist solution. The positive resist solutionsprepared were evaluated by the following methods, and the results areshown in Table 3.

[Image Performance Test]

(Exposure Condition (1))

An organic antireflection film, ARC29A (produced by Nissan ChemicalIndustries, Ltd.), was coated on a silicon wafer and baked at 205° C.for 60 seconds to form a 78-nm antireflection film, and the positiveresist solution prepared above was coated thereon and baked at 120° C.for 60 seconds to form a 160-nm resist film. The obtained wafer wassubjected to pattern exposure by using an ArF excimer laser scanner(PAS5500/1100, manufactured by ASML, NA: 0.75, σo/σi: 0.85/0.55).Thereafter, the resist film was heated at 120° C. for 60 seconds,developed with an aqueous tetramethylammonium hydroxide solution (2.38mass %) for 30 seconds, rinsed with pure water and spin-dried to obtaina resist pattern.

(Exposure Condition (2))

This condition is for forming a resist pattern by an immersion exposuremethod using pure water.

An organic antireflection film, ARC29A (produced by Nissan ChemicalIndustries, Ltd.), was coated on a silicon wafer and baked at 205° C.for 60 seconds to form a 78-nm antireflection film, and the positiveresist solution prepared above was coated thereon and baked at 120° C.for 60 seconds to form a 160-nm resist film. The obtained wafer wassubjected to pattern exposure by using an ArF excimer laser immersionscanner (NA: 0.75). The immersion liquid used was ultrapure water havingan impurity content of 5 ppb or less. Thereafter, the resist film washeated at 120° C. for 60 seconds, developed with an aqueoustetramethylammonium hydroxide solution (2.38 mass %) for 30 seconds,rinsed with pure water and spin-dried to obtain a resist pattern.

[Profile]

The profile of the obtained pattern was observed by a scanning electronmicroscope (S-9260, manufactured by Hitachi, Ltd.) and evaluated.

[Pattern Collapse]

An exposure amount for reproducing a 90-nm line-and-space 1:1 patternwas defined as an optimal exposure amount, and the line width at which apattern, that is, a dense pattern having a line-and-space ratio of 1:1or an isolated pattern having a line-and-space ratio of 1:10, isresolved without collapse to a finer mask size than that when exposedwith an optimal exposure amount, was defined as a threshold patterncollapse line width (nm). A smaller value reveals that a finer patternis resolved without collapse and pattern collapse is less liable tooccur.

[Followability of Water]

The positive resist composition prepared was coated on a silicon waferand baked at 120° C. for 60 seconds to form a 160-nm resist film.Subsequently, as shown in FIG. 1, pure water 2 was filled between thepositive resist solution-coated wafer 1 and a quartz glass substrate 3.

In this state, the quartz glass substrate 3 was horizontally moved(scan) with respect to the surface of the positive resistsolution-coated wafer 1, and the pure water 2 following it was observedwith an eye. The scan speed of the quartz glass substrate 3 wasgradually increased, and the followability of water was evaluated bydetermining the scan speed limit (nm/sec) where a water droplet startsremaining on the receding side due to failure of the pure water 2 infollowing the scan speed of the quartz glass substrate 3. A larger speedlimit allowing for scanning indicates that water can follow a higherscan speed and the followability of water on the resist film is better.TABLE 5 Evaluation Results Composition Normal Immersion Resin PhotoacidBasic Exposure Exposure Follow- (A) Generator Solvent Compound Resin (C)Surfactant Pattern Pattern ability (2 g) (mg) (mass ratio) (mg) (mg) (wt%) (mg) Profile collapse Profile collapse of Water Example 1 1 z2SL-4/SL-2 N-5 C-1 W-1 rectan- 30 rectan- 30 200 (80) 40/60 (7) (20)(1.0) (3) gular gular Example 2 2 z51 SL-2/SL-4/SL-6 N-6 C-1 W-3 rectan-30 rectan 30 200 (80) 40/59/1 (6) (100) (4.8) (3) gular gular Example 33 z2/Z55 SL-2/SL-4 N-3 C-3 W-1 rectan- 30 rectan- 30 200 (20/100) 70/30(6) (100) (4.7) (3) gular gular Example 4 4 z9 SL-2/SL-4 — C-1 W-1slight T- 30 slight T- 30 200 (100) 60/40 (2) (0.1) (5) top top Example5 5 z65/Z9 SL-3/SL-4 N-6 C-3 W-3 rectan- 35 slight T- 35 150 (20/80)30/70 (10) (30) (1.4) (4) gular top Example 6 6 z44/Z65 SL-2/SL-4/SL-5N-1 C-3 W-1 rectan- 35 rectan- 37 150 (25/80) 40/58/2 (7) (30) (1.4) (4)gular gular Example 7 7 z55/z47 SL-1/SL-2 N-4 C-4 W-2 rectan- 35 rectan-35 150 (30/60) 60/40 (13) (20) (0.9) (4) gular gular Example 8 8 z44SL-1/SL-2 N-3 C-5 W-2 rectan- 35 rectan- 40 250 (80) 60/40 (6) (50)(2.4) (4) gular gular Example 9 9 z65 SL-2/SL-4/SL-6 N-2 C-5 W-3 rectan-28 rectan- 28 250 (100) 40/59/1 (9) (10) (0.5) (3) gular gular Example10 10 z15/z37 SL-2/SL-4/SL-6 N-6 C-6 — rectan- 30 rectan- 32 250 (80/50)40/59/1 (10) (8) (0.4) gular gular Example 11 11 z2 SL-2/SL-4 N-1 C-6W-4 rectan- 28 rectan- 28 250 (80) 60/40 (7) (20) (1.0) (3) gular gularExample 12 12 z55/z65 SL-1/SL-2 N-3 C-7 W-4 rectan- 28 rectan- 28 250(40/60) 50/50 (6) (20) (0.9) (3) gular gular Example 13 13 z2/z15SL-2/SL-4/SL-6 N-6 C-8 W-4 rectan- 30 rectan- 30 150 (40/60) 40/59/1(10) (15) (0.7) (5) gular gular Example 14 14 z25 SL-2/SL-4/SL-6 N-1 C-9W-2 rectan- 40 rectan- 40 150 (120) 40/59/1 (7) (50) (2.3) (5) gulargular Example 15 15 z2 SL-2/SL-4 N-1 C-10 W-1 rectan- 35 rectan- 45 100(100) 60/40 (7) (30) (1.4) (3) gular gular Comparative 1 z2 SL-2/SL-4N-5 — W-1 film loss 80 film loss 80 50 Example 1 (100) 60/40 (7) (5)Comparative 1 z51 SL-2/SL-4 N-2 C-1 W-1 T-top 80 T-top 80 200 Example 2(100) 60/40 (10) (500) (23.6) (5)

The symbols in Table 5 denote the followings.

-   N-1: N,N-Dibutylaniline-   N-2: N,N-Dihexylaniline-   N-3: 2,6-Diisopropylaniline-   N-4: Tri-n-octylamine-   N-5: N,N-Dihydroxyethylaniline-   N-6: 2,4,5-Triphenylimidazole-   W-1: Megafac F176 (produced by Dainippon Ink & Chemicals, Inc.)    (fluorine-containing)-   W-2: Megafac R08 (produced by Dainippon Ink & Chemicals, Inc.)    (fluorine- and silicon-containing)-   W-3: Polysiloxane polymer KP-341 (produced by Shin-Etsu Chemical    Co., Ltd.) (silicon-containing)-   W-4: Troysol S-366 (produced by Troy Chemical)-   W-5: PF656 (produced by OMNOVA) (fluorine-containing)-   W-6: PF6320 (produced by OMNOVA) (fluorine-containing)-   SL-1: Cyclohexanone-   SL-2: Propylene glycol monomethyl ether acetate-   SL-3: Ethyl lactate-   SL-4: Propylene glycol monomethyl ether-   SL-5: γ-Butyrolactone-   SL-6: Propylene carbonate

As seen from the results in Table 5, the positive resist composition ofthe present invention is excellent with respect to profile and patterncollapse at normal exposure and immersion exposure and assured ofexcellent followability of water at the immersion exposure.

Examples 16 to 28 and Comparative Examples 3 to 4

<Preparation of Resist>

The components shown in Table-6 below were dissolved in a solvent toprepare a solution having a solid content concentration of 6 mass %, andthe obtained solution was filtered through a 0.1-μm polyethylene filterto prepare a positive resist solution. The positive resist solutionsprepared were evaluated by the following methods, and the results areshown in Table 6.

[Image Performance Test]

(Exposure Condition (1))

An organic antireflection film, ARC29A (produced by Nissan ChemicalIndustries, Ltd.), was coated on a silicon wafer and baked at 205° C.for 60 seconds to form a 78-nm antireflection film, and the positiveresist solution prepared above was coated thereon and baked at 120° C.for 60 seconds to form a 160-nm resist film. The obtained wafer wassubjected to pattern exposure by using an ArF excimer laser scanner(PAS5500/1100, manufactured by ASML, NA: 0.75, σo/σi: 0.85/0.55).Thereafter, the resist film was heated at 120° C. for 60 seconds,developed with an aqueous tetramethylammonium hydroxide solution (2.38mass %) for 30 seconds, rinsed with pure water and spin-dried to obtaina resist pattern.

(Exposure Condition (2))

This condition is for forming a resist pattern by an immersion exposuremethod using pure water.

An organic antireflection film, ARC29A (produced by Nissan ChemicalIndustries, Ltd.), was coated on a silicon wafer and baked at 205° C.for 60 seconds to form a 78-nm antireflection film, and the positiveresist solution prepared above was coated thereon and baked at 120° C.for 60 seconds to form a 160-nm resist film. The obtained wafer wassubjected to pattern exposure by using an ArF excimer laser immersionscanner (NA: 0.75). The immersion liquid used was ultrapure water havingan impurity content of 5 ppb or less. Thereafter, the resist film washeated at 120° C. for 60 seconds, developed with an aqueoustetramethylammonium hydroxide solution (2.38 mass %) for 30 seconds,rinsed with pure water and spin-dried to obtain a resist pattern.

[Profile]

The profile of the obtained pattern was evaluated by observing itthrough a scanning electron microscope (S-9260, manufactured by Hitachi,Ltd.).

[Pattern Collapse]

An exposure amount for reproducing a 90-nm line-and-space 1:1 maskpattern was defined as an optimal exposure amount, and the line width atwhich a pattern, that is, a dense pattern having a line-and-space ratioof 1:1 or an isolated pattern having a line-and-space ratio of 1:10, isresolved without collapse to a finer mask size when exposed with anoptimal exposure amount, was defined as a threshold pattern-collapseline width (nm). A smaller value reveals that a finer pattern isresolved without collapse and pattern collapse is less liable to occur.

[Followability of Water]

The positive resist solution prepared was coated on a silicon wafer andbaked at 120C for 60 seconds to form a 160-nm resist film. Subsequently,as shown in FIG. 1, pure water 2 was filled between the obtainedpositive resist solution-coated wafer 1 and a quartz glass substrate 3.

In this state, the quartz glass substrate 3 was horizontally moved(scan) with respect to the surface of the positive resistsolution-coated wafer 1, and the pure water 2 following it was observedwith an eye. The scan speed of the quartz glass substrate 3 wasgradually increased, and the followability of water was evaluated bydetermining the scan speed limit (nm/sec) where a water droplet startsremaining on the receding side due to failure of the pure water 2 infollowing the scan speed of the quartz glass substrate 3. A larger speedlimit allowing for scanning indicates that water can follow a higherscan speed and the followability of water on the resist film is better.

[Evaluation of Sensitivity]

An antireflection film (ARC25, produced by Brewer Science Co., Ltd.) wasuniformly coated on a silicon substrate by a spin coater to a thicknessof 600 angstrom and dried at 190° C. for 240 seconds. Thereafter, eachpositive resist composition was coated by a spin coater, and the waferwas dried under heating at 115° C. for 60 seconds to form a resist filmof 0.25 μm. The sensitivity of this resist film at the exposure of 193nm was evaluated by using an immersion exposure/dissolution behavioranalyzer IMES-5500 (manufactured by Litho Tech Japan Corp.) equippedwith a 193-nm laser and using water as the immersion liquid.

The sensitivity as used herein indicates a minimum exposure amount ofgiving a film thickness of 0 when the wafer after exposure was driedunder heating at 120° C. for 90 seconds, developed at 23° C. for 30seconds by using an aqueous 2.38 mass % tetramethylammonium hydroxidesolution, rinsed with pure water for 30 seconds and dried and then, thefilm thickness was measured. TABLE 6 Composition Photoacid GeneratorSolvent Basic Compound Resin (C) Resin (2 g) (mg) (mass ratio) (mg) (mg)(wt %) Surfactant (mg) Additive (H) (mg) Example 16 2 z51 SL-2/SL-4/SL-6N-6 C-1 W-3 — (80) 40/59/1 (6) (150) (7.2) (3) Example 17 7 z55/z47SL-1/SL-2 N-4 C-11 W-2 — (30/60) 60/40 (13) (20) (0.9) (4) Example 18 16z55/z51 SL-2/SL-4 N-1 C-2 W-4 — (45/45) 60/40 (10) (50) (2.3) (2)Example 19 17 z55/Z23 SL-2/SL-4 N-5/N-1 C-12 W-4 — (100/25) 60/40 (7/7)(50) (2.3) (2) Example 20 18 z55/Z65 SL-2/SL-4 N-5/N-1 C-13 W-4 —(75/75) 60/40 (7/7) (50) (2.3) (2) Example 21 19 z2 SL-2 N-7 C-14 W-3 —(80) 100 (7) (50) (2.3) (2) Example 22 20 z2 SL-1 N-7 C-15 W-1 — (80)100 (7) (50) (2.3) (2) Example 23 21 z23/z74 SL-2/SL-5 N-3 C-16 W-1 —(50/50) 60/40 (6) (100) (4.7) (2) Example 24 22 z2/z42 SL-2/SL-5 N-3C-17 W-1 — (50/40) 60/40 (6) (100) (4.7) (2) Example 25 23 z2 SL-2/SL-3N-7 C-18 W-1 — (80) 60/40 (7) (100) (4.7) (2) Example 26 24 z2/z15SL-/SL-3 N-4 C-19 W-1 — (50/75) 60/40 (6) (120) (5.6) (3) Example 27 25z30/z12 SL-2 N-8 C-20 W-1 — (50/75) 100 (7) (120) (5.6) (2) Comparative1 z9 SL-2/SL-4/SL-6 N-2 C-1 W-1 — Example 28 (100) 40/59/1 (10) (300)(14.2) (5) Comparative 9 z65 SL-2/SL-4/SL-6 N-2 — W-3 H-1 Example 3(100) 40/59/1 (9) (3) (5) Comparative 1/9 z65 SL-2/SL-4/SL-6 N-2 — W-3 —Example 4 (1/1) (100) 40/59/1 (9) (3) Evaluation Results Normal ExposureImmersion Exposure Followability of Profile Pattern collapse ProfilePattern collapse Sensitivity, mJ Water Example 16 rectangular 40rectangular 40 6.0 200 Example 17 rectangular 28 rectangular 28 6.0 250Example 18 rectangular 30 rectangular 30 6.5 230 Example 19 rectangular28 rectangular 28 6.7 200 Example 20 rectangular 30 rectangular 30 6.0250 Example 21 rectangular 30 rectangular 30 6.5 250 Example 22rectangular 28 rectangular 28 6.7 250 Example 23 rectangular 30rectangular 30 6.0 250 Example 24 rectangular 28 rectangular 28 6.0 250Example 25 rectangular 33 rectangular 33 6.5 250 Example 26 rectangular30 rectangular 30 6.0 230 Example 27 rectangular 29 rectangular 29 6.0240 Comparative Slight T-top 50 Slight T-top 50 6.0 200 Example 28Comparative rectangular 80 rectangular 80 6.0 50 Example 3 Comparativerectangular 80 rectangular 80 6.0 50 Example 4

The symbols in Table 6 denote the followings.

-   N-1: N,N-Dibutylaniline-   N-2: N,N-Dihexylaniline-   N-3: 2,6-Diisopropylaniline-   N-4: Tri-n-octylamine-   N-5: N,N-Dihydroxyethylaniline-   N-6: 2,4,5-Triphenylimidazole-   W-1: Megafac F176 (produced by Dainippon Ink & Chemicals, Inc.)    (fluorine-containing)-   W-2: Megafac R08 (produced by Dainippon Ink & Chemicals, Inc.)    (fluorine- and silicon-containing)-   W-3: Polysiloxane polymer KP-341 (produced by Shin-Etsu Chemical    Co., Ltd.) (silicon-containing)-   W-4: Troysol S-366 (produced by Troy Chemical)-   W-5: PF656 (produced by OMNOVA) (fluorine-containing)-   W-6: PF6320 (produced by OMNOVA) (fluorine-containing)-   SL-1: Cyclohexanone-   SL-2: Propylene glycol monomethyl ether acetate-   SL-3: Ethyl lactate-   SL-4: Propylene glycol monomethyl ether-   SL-5: γ-Butyrolactone-   SL-6: Propylene carbonate

Additive (H-1) used in Comparative Example 3 is a compound used forcomparison and contrast with the resin as the component (C).

As seen from the results in Table 6, the positive resist composition ofthe present invention is excellent with respect to the profile andpattern collapse at normal exposure and immersion exposure andfurthermore, is excellent with respect to the followability of water andsensitivity at the immersion exposure.

According to the present invention, a positive resist compositionimproved in the profile and pattern collapse and a pattern formingmethod using the positive resist composition can be provided.Furthermore, a positive resist composition suitable for immersionexposure, ensuring that the profile and pattern collapse are not changedat immersion exposure and the followability for water is good, and apattern forming method using the positive resist composition, can beprovided.

The entire disclosure of each and every foreign patent application fromwhich the benefit of foreign priority has been claimed in the presentapplication is incorporated herein by reference, as if fully set forth.

1. A positive resist composition, which comprises: (A) a resin having amonocyclic or polycyclic alicyclic hydrocarbon structure, of whichsolubility in an alkali developer increases under an action of an acid;(B) a compound capable of generating an acid upon irradiation withactinic rays or radiation; (C) a resin having a repeating unitrepresented by formula (C); and (D) a solvent, wherein a content of theresin as the component (C) is from 0.1 to 20 mass % based on a solidcontent of the positive resist composition:

wherein X₁, X₂ and X₃ each independently represents a hydrogen atom, analkyl group or a halogen atom; L represents a single bond or a divalentlinking group; and Rp₁ represents an acid-decomposable group.
 2. Thepositive resist composition according to claim 1, wherein the resin asthe component (C) further has a repeating unit represented by formula(C2):

wherein X₄, X₅ and X₆ each independently represents a hydrogen atom, analkyl group or a halogen atom; L₁ represents a single bond or a divalentlinking group; and Rp₂ represents a non-acid-decomposable group.
 3. Thepositive resist composition according to claim 1, wherein a content ofthe resin as the component (C) is from 0.1 to 5 mass % based on a solidcontent of the positive resist composition.
 4. The positive resistcomposition according to claim 1, wherein formula (C) is represented byformula (C1):

wherein X₁, X₂ and X₃ each independently represents a hydrogen atom, analkyl group or a halogen atom; and R₁₂, R₁₃ and R₁₄ each independentlyrepresents an alkyl group, a cycloalkyl group, an alkenyl group or anaryl group, or a monovalent group formed by bonding at least two ofthese groups, provided that at least one of R₁₂, R₁₃ and R₁₄ representsan alkyl group, and two members out of R₁₂, R₁₃ and R₁₄ may combine toform a ring.
 5. The positive resist composition according to claim 4,wherein in formula (C1), R₁₂, R₁₃ and R₁₄ each independently representsan alkyl group or an alkenyl group and at least one of R₁₂, R₁₃ and R₁₄represents an alkyl group.
 6. The positive resist composition accordingto claim 1, wherein the resin as the component (C) comprises a repeatingunit represented by formula (C1) and a repeating unit represented byformula (C2) in a proportion of from 80 to 100 mol % in total repeatingunits:

wherein X₁, X₂, X₃, X₄, X₅ and X₆ each independently represents ahydrogen atom, an alkyl group or a halogen atom; R₁₂, R₁₃ and R₁₄ eachindependently represents an alkyl group, a cycloalkyl group, an alkenylgroup or an aryl group, or a monovalent group formed by bonding at leasttwo of these groups, provided that at least one of R₁₂, R₁₃ and R₁₄represents an alkyl group, and two members out of R₁₂, R₁₃ and R₁₄ maycombine to form a ring; L₁ represents a single bond or a divalentlinking group; Rp₂ represents a non-acid-decomposable group; and m and neach represents a molar ratio of the repeating unit, and m=10 to 100,n=0 to 90 and m+n=100.
 7. The positive resist composition according toclaim 1, wherein the resin as the component (C) comprises at least onerepeating unit selected from formulae (C-I) to (C-IV) in a proportion offrom 80 to 100 mol % in total repeating units, provided that therepeating unit represented by formula (C-I) is used in combination withthe repeating unit represented by formula (C-II):

wherein R₁ represents a hydrogen atom or a methyl group; R₂ represents ahydrocarbon group having two or more —CH₃ partial structures, providedthat when a plurality of R₂'s are present, the plurality of R₂'s may bethe same or different; P₁ represents a single bond, an alkylene group oran ether group, or a linking group having two or more thereof; P₂represents a linking group selected from —O—, —NR— and —NHSO₂—, whereinR represents a hydrogen atom or an alkyl group; x1, x2, y and zrepresent mol % in total repeating units, and x1 represents a number of0 to 50, x2 represents a number of 0 to 50, y represents a number of 0to 100, z represents a number of 0 to 100, provided that x1, x2, y and zsatisfy 80≦x1+x2+y+z≦100; and n represents an integer of from 1 to
 4. 8.The positive resist composition according to claim 1, wherein the resin(A) contains at least a (meth)acrylate-based repeating unit having alactone structure and a (meth)acrylate-based repeating unit having anacid-decomposable group.
 9. The positive resist composition according toclaim 1, wherein the resin as the component (A) has a repeating unitrepresented by formula (A1), a repeating unit represented by formula(A2) and a repeating unit represented by formula (A3):

wherein Xa, Xb, and Xc each independently represents a hydrogen atom ora methyl group; R₁ represents a monovalent organic group having alactone structure; R₂ represents a monovalent organic group having ahydroxyl group or a cyano group; and R₃ represents a group capable ofbeing detached under an action of an acid.
 10. A pattern forming method,which comprises: forming a resist film from a positive resistcomposition according to claim 1; and exposing and developing the resistfilm.
 11. The pattern forming method according to claim 10, wherein theexposure is preformed through an immersion liquid.
 12. The positiveresist composition according to claim 1, wherein the compound as thecomponent (B) has a triphenylsulfonium cation structure.
 13. Thepositive resist composition according to claim 1, which furthercomprises a surfactant.
 14. The positive resist composition according toclaim 1, which further comprises a basic compound.